Peek-a-Boo! (And Other 9 Month-Old Milestones)

This is for information only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. Full disclaimer here.

Nine months! What skills do we expect a nine month-old baby to learn? Did you know most of a nine month-old’s milestones can be linked to the game of peekaboo? 

Individual learning and skills vary a lot, but there are a few key things we look for at specific ages. These are the so-called milestones. Today’s post covers major milestones of nine month-old babies, including the updated 2022 Centers for Disease Control and Prevention (CDC) guidelines, as well as a few more “milestones” pediatricians and parents might observe. 

As always, this article cannot evaluate or diagnose any individual child’s development (delays or otherwise). This is just general information so that parents can anticipate around what age their child may enjoy different activities (ahem, peekaboo). It may also help caregivers better appreciate all that their baby is learning! If you are worried about development or milestones, please see your child’s pediatrician. 

But first, Peek-a-boo

Babies at age nine months may start to enjoy a game of peek-a-boo. It involves a few key areas of development including social and emotional development, cognitive development, and even some motor skills.

What exactly do we mean by peek-a-boo?

Allow me to explain. 

The game of peek-a-boo involves a baby seeing someone’s face. Joy! How fun! Then, the person’s face is briefly hidden, whether behind their hands, a blanket, or just ducked out of sight.

A pivotal moment follows.

A second or two later, the face is revealed again, often with the words, “peek-a-boo!”

During those few seconds of the face being hidden, a younger baby (one who hasn’t yet reached this milestone of enjoying peek-a-boo) may think their beloved is gone forever. Or just: gone. They cannot be seen. Therefore they do not exist. 

However, at around nine months of age, babies begin to learn the idea of “object permanence,.” This is the idea that something can still exist even if it isn’t visible right this second. 

This means that for these older babies, the game of peek-a-boo isn’t stressful (“my parent is gone”) or boring (nothing to see here), it’s delightful. (“I know my parent still exists! When and how will they reveal themselves again?!”) The anticipation is brief and fun.

The big reveal and the face coming into sight again with an exuberant “peek a boo,” is like a mini surprise and a joyful reunion all in one. 

If a baby enjoys this game, they can repeat as needed, as long as parental endurance allows. 

With this in mind, here are other milestones at age nine months. Many can be supported or fostered with peek-a-boo. 

Social and Emotional Milestones of 9 Month-old Babies

1. Delight in another person. At around nine months of age many babies have the social-emotional development to enjoy someone else’s company (making eye contact, smiling when they smile, giggling with someone else). These are also all key skills to enjoying a game of peek-a-boo. The months of a parent cooing and smiling at their baby start to pay off as a nine month-old responds in more complex ways. 
2. Related to this, babies may start to clearly show facial expressions to communicate a variety of emotions. Newborns are often either content or crying. By 9 months of age, babies may look sad or angry or surprised. Or happy! Especially during a game of peek-a-boo when their beloved’s face returns. 
3. Respond when a caregiver leaves. By this age, babies may show some kind of response to when their parent leaves. At younger ages, many babies immediately react to what they can see and who is now caring for them. At this age, someone can still be on their mind even if they’re actively leaving. They can sense that absence. It can be rough! So, this is around the age babies start to cry when a parent or other caregiver leaves a room. Some people call this “separation anxiety,” but it is a very normal part of typical development. 

Back to the idea of peekaboo, these babies have the cognitive ability to know that someone still exists even if their face is briefly covered. 

This is also the age where if a child is playing with a toy and someone else hides the toy, the baby will search for the toy. 

4. The CDC includes “smiling and laughing” during peekaboo as an official milestone. It symbolizes so much! This is also why just being aware of milestones can help support your child’s development. Give peekaboo a try. 

5. By age nine months (and often earlier), babies look when called by name. Talking/singing through a game of peekaboo helps support this. “Where is Baby Aileen?” followed by revealing the face. “There she is! Hello, Aileen!”

Language Milestones at Age 9 Months

1. This can be such a delightful age as babies learn how to make different sounds with consonants. For example: “Mamamama. Dadadadada.” At this age, the sounds don’t always correspond with a specific person. That happens closer to age 1 year. But again, repeating the phrases helps guide the baby to eventually knowing who “mamama” is. In peek-a-boo, it may sound like: “Where is Mama? Peek-a-boo! Here I am!”

2. By nine months of age, babies also physically respond to their caregivers, raising their arms, often in anticipation of being picked up or held. An energetic caregiver could certainly choose to incorporate this into a peek-a-boo game. Lifting or swinging or hugging upon the reunification. 

Cognitive Milestones at Age 9 Months

The CDC mentions two “thinking milestones.”

1. The first is the idea of object permanence, mentioned earlier. Babies look for a toy that has been moved out of sight. 
2. The second is banging two objects together, like blocks or other toys, (especially those with a satisfying sound). I always encourage free time outside for babies and children, especially when supporting development (see these posts for specifics on 18 month-olds and 5 year-olds). Outdoors is the perfect place to experiment banging different types of objects together. Sticks and leaves can result in very different sound experiments.

Physical (Motor) Milestones at Age 9 Months

People often want to know about crawling. It’s no longer an official milestone (see this post on baby motor development), but many babies do move about on their hands and knees, crawling, around this age. There are, however, a few more specific ones that pediatricians and parents can watch for. You’ll see that many show signs of growing independence, like sitting on their own.

Gross Motor Milestones in 9 Month-Old Babies

1. Get into a sitting position on their own. Whether a baby has been crawling or laying on their tummy, by nine months of age, many can maneuver their body into a seated position without any outside help, like a caregiver’s supportive hands. 
2. Sit without support. For many months of a baby’s life, they may sit propped up against a parent’s chest while being held or leaning up against a pillow. Sometimes they gently topple over as they reach for an object or shift their weight. They’re just not steady enough yet. However, by nine months, they can more reliably sit solo, usually without toppling.
3. For what it’s worth (I love noticing these little changes and share in case you also like to appreciate a few extra details), this is also the age when a baby’s back seems to be more straight when they sit. Previously, they had much more rounded backs when they sat. (As I’ve mentioned before, gross motor milestones usually need a lot of time and space for babies to figure out and develop). 

Fine Motor Skills at Age 9 Months

Fine motor skills involve the smaller muscles, usually referring to the hands and fingers.

1. Pass an object from one hand to another. Whether it’s a toy or a piece of scrambled egg, babies at 9 months start to move objects from one side to the other. They’ve finally developed the coordination, the hand dexterity, and the eye development to complete this task. 

To incorporate peek-a-boo, a family could play with a favorite toy hiding under a blanket then having the toy “jump” out. Then, allow the baby to play with the toy however they’d like, which eventually may include passing it between their hands. 

2. Use hands to bring an object closer with a “raking motion.” This is also a fun one to watch develop. Simply by placing a toy or snack slightly out of reach, the baby can stretch out their hand and try to bring it closer. It’s one of those things that many babies need a lot of attempts with before conquering it. 

Both of these skills develop over time with a lot of different activities, objects, and practice. As mentioned, playing outside is good for development, especially in these examples of fine motor skills. They can reach for sticks and leaves, passing them between their hands, while enjoying natural light, under close adult supervision of course. 

Summary: Peek-a-boo helps support development in babies, especially around 9 months of age.

Nine months is an age of joy and real wonder. (To be clear, it’s not without challenges of course). By incorporating regular play with an attentive adult, babies can thrive. If an adult needs a particular “activity,” a game of peek-a-boo is an amazing excellent start. 

Maya M. Mahmood, D.O., FAAP is a board-certified pediatrician and mom. She is passionate about parents having evidence-based information to help their families be healthier.