For young babies, out of sight is definitely out of mind. And that goes for everyone and everything — including your baby's teddy bear, blanket and even his caregivers.

But by the time your little one is about 8 months old, if not even earlier, he'll start to understand an important concept: that favorite toys, people and other things still exist even when they're not in plain view. That awareness is known as object permanence, and it represents a huge leap in your baby’s thinking.

What is object permanence?

Objective permanence is an important cognitive milestone reached when your baby begins to understand that a toy, parent, or other familiar person or item still exists even if he can't see it. First discovered by a psychologist named Jean Piaget, object permanence means that your baby is starting to be able to imagine or "see" a person or thing in his mind, even if it's not there in front of him.

This explains why when you put your baby’s teether behind your back, he cranes his neck to see where it went — and why games like hide-and-seek and peekaboo, for example, are so exciting. (Now you see me, now you don’t!)

As your baby starts to better understand this concept, he’ll also start to miss you when you’re gone. He realizes that when you walk out of the room, you haven’t left for good.

When does object permanence develop?

Like most baby skills, your child has been building toward this particular awareness for his entire life. Here are a few other concepts that develop before object permanence does, and when they appear:

  • Newborns: Facial recognition. Even the youngest infants prefer looking at human faces.
  • 3 months: Object recognition. Around this age, babies develop object recognition, a term that means your cutie can distinguish the many familiar things in his life, like books or his favorite squishy toy. He probably won’t know the names yet, but in a few months he’ll understand what you mean by “book” or “diaper.”
  • 4 to 6 months: Cause and effect. Around this age, your little one will discover a new game: Tossing toys and food from his crib or the high chair. This teaches him cause and effect (he drops, you pick up). But you’ll also notice he’ll start to look for objects that have gone overboard. This is his budding sense of object permanence (“Hey! Maybe that binky isn’t gone for good!”).
  • 8 to 9 months: Looks for hidden objects. If your baby sees you hide an object, he'll now understand that it's not gone for good and will try to search for it.
  • By 12 months: By the time he celebrates his first birthday, your little one will be able to easily find objects he sees you hide.

How did Jean Piaget study object permanence?

Jean Piaget was a Swiss psychologist during the mid-20th century who studied how kids learned to understand the world around them. His theory, based on hands-on research, was that children’s minds developed in set stages from infancy until the age of 18.

Piaget’s theory of object permanence arose, in part, after he hid a toy under a blanket and noticed that only babies who were 8 months and older looked for the toy under the blanket. His conclusion: Around 8 months, babies have the ability to form an image of the toy (or person) in their mind, something younger babies can’t do. 

Experts now think babies begin forming these mental images even earlier, but they might not look for the hidden toy because they either don’t have the physical ability to reach for it or because they become distracted. 

What is the relationship between object permanence and separation anxiety?

As your baby learns about object permanence, he may also start to show signs of separation anxiety. Why? Now your baby knows that when you leave the room or the house, you’re not gone forever. But he doesn’t know when you’ll be back (the concept of “time” will come later). That makes him anxious — he wants you to come back right now!

Separation anxiety can set it in as early as 7 months, but it may peak anytime between 9 and 18 months. Of course, not all babies suffer from separation anxiety. A lot depends on your little one’s temperament and even the time of day — separation anxiety can get worse when your cutie is tired, hungry or out of sorts. Having good-bye rituals and being specific about when you’ll be back (after naptime, say, or before lunch) will help soothe your sweetie as he turns into a toddler. 

What’s the difference between separation anxiety and stranger anxiety? Stranger anxiety commonly starts between 6 and 9 months of age, when babies realize that their parents are the VIPs in their lives. Anyone else just doesn’t measure up now, even grandparents, so your baby might make his displeasure known even when he’s in your arms.

Games to help your child understand object permanence

Playing with your baby is the best way to help him master new skills, and object permanence is no exception. Not only does your little one love games like peekaboo, but they're good for his brain. They help him understand that you’ll be coming back when you leave, which can be comforting during the tough separation anxiety phases.

Here are two classic games to try:

Peekaboo

You were probably playing this classic when you were a tot, so you know what to do: Cover your face with your hands, then open them as you say, “Peekaboo!”

Of course, you can cover your face with anything — a blanket, your sweater, a clean diaper. When he gets a bit older, hide your entire head with a blanket, and let your baby pull it off you. You can also show your little one how to hide his face so he can get in on the fun. 

Hide-and-seek

There are endless variations to this game, using toys or yourself. Babies and toddlers love finding objects, and hide-and-seek games (along with peekaboo) help boost their rapidly developing brains. Let your 8- or 9-month old watch you hide a toy under a pillow or blanket, but leave some of the toy sticking out in plain view. Then let him find it. 

When he’s a bit older, you can hide the toy completely. At 10 months old, many babies will continue looking for a toy that you’ve hidden in an obvious place.

Toddlers also love hide-and-seek, but add some action into it for your newly minted walker. Take turns hiding with a short chase after you’ve found each other.

Grasping the concept of object permanence might not be as showy a milestone as pulling to stand or walking, but it’s incredibly important. It’s a sign that your baby now has the memory and the ability to think abstractly, which helps set the groundwork for that other show-stopper coming soon: saying his first words.