Apr 26, 2024
Apr 30, 2024
Developmental milestones
April 30, 2024
Developmental milestones

Newborn to toddler: a complete guide on baby milestones

Change is a constant in your child’s first year of life. Your little one is growing non-stop, you’re learning as fast as you can, and everyone’s just trying to keep up. Given the quick pace of this season, it can be hard to know what to expect and when. But staying on top of child development during year one is super important. How well your baby is meeting newborn milestones gives you clues about their growth and how you and their pediatrician can continue to help them. In this guide we’ll give you a detailed breakdown of what to expect during the newborn phase, infancy, and the transition from infancy to toddlerhood, plus some guidance on age ranges so you know when your baby moves from one stage to the next.

The first year and beyond: understanding newborn, infant, and toddler age ranges

So many words we use to describe babies and small children are used interchangeably. So before we hop into developmental milestones, let’s clarify when your child is considered a newborn, an infant, or a toddler. 

What is the newborn phase, and what age is considered a newborn? 

During the newborn phase, a baby is getting used to being in the real world. Per the World Health Organization (WHO), the newborn phase lasts for a baby’s first 28 days of life — that is, the first month after birth. 

Some people think a baby is a newborn through the first 8 weeks (two months) after birth. And many medical experts consider the baby’s first 12 weeks (three months) after birth — also known as “the fourth trimester” — to be the newborn age range. In other words, the definition of a newborn isn’t so cut and dry, and might depend on who you ask.

What is the infant age range?

A baby is an infant through their first full year of life, from 0 months to 1 year. This means there’s some overlap between the terms “newborn” and “infant” since infancy also includes the newborn phase. 

During the first one to 3 months of a baby’s life, either of the words “newborn” or “infant” could be used to describe the baby. You might even hear the combination “newborn infant.”

What is the toddler age range?

After infancy, a child becomes a toddler. You can consider a child’s first birthday a promotion into toddlerhood. (Simultaneously heart-warming and gut-wrenching, right?!) Kids are considered toddlers from the time they turn one through about 3 years old. 

What age is no longer a toddler, and what is the difference between toddler and preschooler?

Between 3 and 5 years old, a child is no longer a toddler, but a preschooler. By this time, they’re skill growing physically, but perhaps not as much as you’re used to. Instead, so much energy is going into their mental and emotional growth and development. Many children who aren’t already enter school settings during this time, hence the reference to preschool.

Newborn Infant Milestones, Week by Week

There can be a bit of a learning curve when it comes to caring for a newborn, especially if you’ve never done it before. As the parent of a newborn, you’re both at a point where they’re adjusting to life outside the uterus and you're both trying to figure each other out. Everything is new, which can be overwhelming. 

Before hopping directly into the milestones, it's worth getting an understanding of two things newborns do all the time: sleep and eat.

Newborn Sleep

Newborns sleep…a lot. In a 24-hour period, newborns get about 16 to 17 hours of sleep. 

Now, that doesn’t mean they always sleep when you want them to. Since their tummies are so small, they have to wake quite often — every few hours or so — to eat. During this time, most babies are not sleeping straight through the night, and may wake up every 3 to 4 hours, or even more often, to eat.

Newborn Eating Habits

In a 24-hour period, most newborns will have 16 to 24 oz of milk, whether breastmilk, formula, or a combination of the two. Breastfed babies may eat more often — 8 to 12 times per day — which is known as cluster feeding. The general rule of thumb is that they should be free to eat as much as they want, on demand.

You'll be advised to keep count of their wet diapers and poop-y diapers, which can let you know whether they're getting enough to eat.

Sleep and good nutrition are vital in the newborn phase as your baby quickly adapts to the world and their bodies work to keep up. Your pediatrician will likely ask you at every checkup or wellness visit about how well your baby is meeting the Centers for Disease Control and Prevention’s developmental milestones. This is called developmental monitoring, which is different from developmental screening. (More on that later!)

Here’s a week-by-week preview of what to expect when it comes to newborn development and developmental milestones. 

Week 1

Baby enters the brand new world, and boy is there a lot going on! There may be very few moments when your little one is awake or has their eyes open during this first week. When they are awake, they may even lift their heads up for short periods to take it all in. 

This week you’ll get familiar with many of baby’s natural reflexes, like the startle reflex (or moro reflex), rooting reflex, and sucking reflex. You’ll also be keeping the baby’s umbilical cord stump clean, looking out for signs of jaundice, trying to help your baby regain the weight they lose in the days after birth, and counting wet and poopy diapers to ensure your baby is eating well enough. 

Week 2

In week 2, most babies will have regained their birth weight. Babies who take formula often regain birth weight more quickly than breastfed babies. If you’re wondering about your baby’s weight, your pediatrician can let you know whether they have cause for concern. If you’re breastfeeding, you and your baby may need more time to get into a good routine, so it may take longer for breastfed babies to regain their weight. But no matter how they’re fed, many newborns’ appetite will increase during week 2. And did I mention...those diapers?!

Week 3

By now, lack of sleep might be making things more difficult for you, but rest assured that your baby is making some significant strides. If the eat-sleep-poop routine feels stale, think about how to spice things up. Singing songs, reading books, and even making silly faces can be helpful stimulation for your child when they’re awake.

Also, it’s never too early to start working on a nighttime routine or sleep routine, even if your little on is still not sleeping for long stretches of time.

Week 4 

Four weeks already! If you haven’t yet, it’s a good time to start practicing tummy time, which should always be supervised by an adult. In the beginning, your baby might not be a fan, but even a minute or two here and there can be helpful. By now, if your baby's weight looks good, your pediatrician may no longer recommend counting diapers, although they'll still make plenty of dirty ones!.

An adorable habit for everyone around this time, your baby may start to practice making sounds with their voice. And even though you won’t be able to make meaning of that voice for a while and it's not quite babbling just yet, "talking back" to them when they want to chat is great for child development and also just terribly cute.

Week 5

Around this time, some newborns (though not all) will start to string together longer stretches of sleep time, which means you may get a bit more rest on your end. Even if you’re still having sleep struggles, creating a sleep routine can help establish good habits for the future. Tummy time will last longer as your baby may be able to tolerate more time, look around in more directions, and focus on objects of different patterns and colors.

Week 6

This week, your baby will continue to eat 24 to 32 ounces per day, but they may be eating less often. Instead of feeding every 2 to 3 hours, you may be able to get by with stretches of 3 to 4 hours in between feedings. 

Week 7

As your baby approaches the 2 month mark, they are likely looking very much like a baby and less like a newborn. It probably helps that they’re likely practicing using their voice more often and hopefully enjoying tummy time more. Don’t forget to continue helping your baby practice those skills which are super important for their physical growth and development.

Week 8

And just like that, you’re 2 months in! By this time, most babies inspect faces closely, get calmer when they hear your voice, and may even smile in response. They also take more interest in their toys and watch people as they move around. During tummy time, 8 week olds usually hold up their heads. They also lose the startle reflex around this time. As they gain weight, you'll notice they may move from one diaper size to the next. At this age, most babies are in newborn diapers or size 1 diapers.

More Info on Newborn Baby Milestones

It can be exciting to experience your child progress through milestones in their first year, but it can also cause you to worry if or when they don’t. 

If you’re ever worried about whether or not your baby is meeting milestones as expected, don’t delay bringing up your concerns with your baby’s pediatrician. Even if you’re not 100% sure, it doesn’t hurt to ask, and Summer Health doctors and specialists are happy to chat through any questions you have. 

If it turns out your baby is progressing well, then you haven’t lost anything by checking. If there may be a developmental delay, your pediatrician should do a developmental screening to get more information. The earlier developmental delays are addressed, the better.

How Can I Help My Newborn Meet Their Newborn Milestones?

We all want the best for our little ones, even from the time they’re tiny, so it’s natural to wonder how you can support your newborn with meeting milestones. Here are just a few ways to support child development in newborns: 

  • Provide them with a loving environment and loving caregivers

  • Help them get the nutrients they need

  • Make time for tummy time, even when it’s hard

  • Stimulate their senses with different textures, colors, and voices

  • Create routines

  • Help them grow socially

  • Monitor child development milestones

  • Make and keep their pediatrics appointments

Major Infant Developmental Milestones by Month

Past the fourth trimester, babies have officially entered their infant era and will remain infants until their first birthday. Infant development milestones from 3 months through 12 months can be lots of fun! 

CDC defines a developmental milestone as something 75% or more children can do by a certain age. Here’s a look at common developmental milestones during infancy. 

Infant Sleep

The American Academy of Sleep Medicine (AASM) recommends infants between 4 and 12 months get 12 to 16 hours of sleep in a 24-hour period. (And the American Academy of Pediatrics agrees!) 

Like during the newborn phase, total sleep time includes naps. Once your baby is an infant, they may start to develop a more predictable sleep schedule, including nap sleep and nighttime sleep.

Infant Eating Habits

Many babies are starting solids between 4 and 6 months, so major changes are happening with eating habits and meal routines.

Four Month Milestones

Most babies around this age will smile on their own, chuckle, or coo to get your attention. If you talk to them, they’ll often make sounds back or at least turn their heads to look at you. Adorably, many four-month-olds start babbling too. Physically, they’re better able to hold toys in their hands and hold their heads steady if you’re holding them.

Six Month Milestones

By their half-birthdays most babies know the people they’re around most often and look at themselves in the mirror. Those adorable baby laughs are also usually a thing by this time. Most babies are also babbling and will make high-pitched squealing noises. Be sure any area your baby is in is childproofed well because 6 month olds are reaching and grabbing for everything and they learn by putting things in their mouths! Many babies are also rolling over from tummy to back by this time.

Nine Month Milestones

At 9 months old, your baby may be in a “stranger danger” season where they are shy or scared around people they don’t know or see very often, and may cry when you’re not around. Most babies at this age recognize their names and will look in response. They’re getting lots of practice with stringing sounds together, even though the sounds are intelligible yet. Physically, most babies sit without support at this stage and can even get into the sitting position on their own. Some babies will start to say dada around this time.

Twelve Month Milestones

Cue the “Happy Birthday” song. You've got a toddler on your hands! By their 1st birthdays, most children can wave goodbye, say “mama” or “dada” to a parent, and put objects in containers. Physically, most children can stand up using something to pull themselves up with and can even walk a few steps while holding onto a large, stable object like furniture. They can also pick up objects — even small ones — using their thumb and pointer fingers. 

Visit CDC’s website for the full list of infant developmental milestones.

Developmental Screenings during Infancy

Unless you ask for your baby to be screened at an earlier age, your baby will have their first developmental and behavioral screening at 9 months. Per CDC, developmental screenings are more formal than standard developmental monitoring of milestones. 

During developmental screening and behavioral screening, your child’s doctor is using questionnaires to assess how well your child is developing in many different areas, including language, behavior, emotions, movement, and more.

A Look Ahead: Toddler Age Range and Toddler Milestones

After the one year mark, your baby — a baby no more! — becomes a toddler. The name is quite fitting since to "toddle" means to walk in short, wobbly steps. While age 1 marks the start of toddlerhood, the end of the toddler age range is a bit fuzzier. Some time around 3 years old, though, tends to be when toddlers are considered preschoolers.

Your Baby’s Transition from Infant to Toddler

Have you met a toddler before? They get into everything! But it’s all a part of them practicing and gaining new skills. While newborns and infants may go through transitions more rapidly, the infant-to-toddler transition can be especially tricky to navigate for parents. Some parents may feel like they’ve just gotten the hang of taking care of a baby, only to realize their child has different needs. It can even be emotional for many parents who notice distinct signs of their little one growing up! 

Major transitions happening during the transition from infant to toddler include:

  • Getting around — first steps: By 15 months, most toddlers have taken their first few steps, and some toddlers may be walking by then.

  • Eating: After age 1, toddlers are getting most of their nutrients from solid foods, along with some type of milk source.

  • Dropping naps - Toddlers need slightly less sleep than infants do. AASM recommends toddlers between ages one and 2 get 11 to 14 hours of sleep in a 24-hour period. These total sleep times still include naps, although toddlers may drop from 2 naps to one, and eventually may drop naps altogether. (Fun facts: almost all preschoolers stop napping by age 5!)

These transitions can be exciting for, and tough on, everyone involved — parents and kids alike. Making sure your toddler gets enough of the basics — affection from caregivers, sleep, nutrients, and social interaction — can go a long way.

Developmental Screenings for Toddlers

During the toddler age range, your little one will have two more developmental screenings, unless you ask for more: one at 18 months and another at 30 months. Toddlers should also have an autism screening at 18 months and 24 months, which will often involve you completing a questionnaire about your child.


While it's important to know about developmental milestones, each baby is different. So naturally, you might have specific questions about your little one.

Your child's pediatrician is a great resource, but between visits, the pediatricians and specialists at Summer Health can offer high-quality, personalized advice. We're just a text away!

Megan N. Freeland, PharmD
Content Writer
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