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It might sound a little clinical, but object permanence is just one of many important developmental milestones you get to enjoy with your little one. In a nutshell, object permanence means your baby understands that things they can't see — you, their cup, a pet — still exist.

If you hide a favorite toy when playing with a very young baby, what happens? They might seem briefly confused or upset but then quickly give up on looking for it. It's quite literally "out of sight, out of mind."

Once your baby has grasped object permanence, though, they'll probably look for the toy or try to get it back — or even loudly voice their displeasure at its disappearance. That's because they know the toy still exists!

The development of object permanence helps your baby reach even more adorable milestones, including:

  • memory development
  • exploration
  • pretend play
  • language acquisition

It can also affect how your baby reacts when you leave the room — sudden tears or a pterodactyl shriek sound familiar? — even if it's just for a quick bathroom trip.

This separation anxiety is also a normal part of development. Playing certain games (like peekaboo) with your baby can help them learn that yes, you're definitely coming back, just like you always have before.

Let's take a closer look at how you can help your little as they develop the idea of object permanence and work through separation anxiety.

Once babies can recognize faces (around 2 months of age) and familiar objects (around 3 months), they begin to understand the existence of these objects.

Then they may start looking for toys you've hidden, have fun uncovering or opening things, and flash that precious toothless grin during games like peekaboo.

Jean Piaget, a child psychologist and researcher who pioneered the concept of object permanence, suggested that this skill doesn't develop until a baby is about 8 months old. But it's now generally agreed that babies begin understanding object permanence earlier — somewhere between 4 and 7 months.

It'll take your baby some time to fully develop this concept. They might go after a hidden toy one day and seem completely uninterested the next day. This is fairly common, so don't worry!

Try not to fret

It's perfectly normal to want your baby to reach much-anticipated developmental milestones early. If they seem a bit behind schedule, it's also normal to wonder why.

You might feel a little concerned if your baby is close to 8 months but still doesn't seem to notice their stuffed toy is hidden under a blanket. But rest easy: Development doesn't happen in the same way for every child, and your baby will reach this milestone in their own time.

It's also been suggested babies who don't search for their toys may just not have much interest in that toy. Let's be honest — many of us would turn our homes upside down looking for our car keys while a missing joker from a deck of cards just isn't worth our time.

If you're worried, though, talking to your child's pediatrician can help relieve any concerns you might have if your baby hasn't picked up on object permanence yet.

The concept of object permanence comes from Piaget's theory of cognitive development. Piaget believed the following:

  • Children can learn by themselves, without help from adults or other children.
  • Children don't need rewards or outside motivation to learn new things.
  • Children use their experiences to develop their knowledge of the world.

From his work with children, he created a stage-based theory of development. Object permanence is a major milestone in the first of four stages — sensorimotor stage. This stage marks the period between birth and age 2.

During this stage, your baby learns to experiment and explore through movement and their senses, since they don't yet understand symbols or abstract thought.

This means a lot of photo-worthy blundering about, falling down, grabbing and throwing all those toys you just picked up, and putting every single thing they can find into their mouths. But it's OK, because this is exactly how babies learn. (And it's exactly the stuff that makes grandmas smile, so be ready to capture these moments and share!)

As we've already covered, Piaget believed understanding of object permanence began around the age of 8 months. But many babies start acquiring this idea much earlier. You might have firsthand proof of this, if your 5-month-old is already grabbing for hidden toys!

Some experts have criticized other areas of Piaget's research. He assumed developmental stages happened for all children at the same time. But scientific evidence now supports the idea that children develop on varied timelines.

Generally speaking, though, Piaget's research has held up well over time, and his ideas on development still hold an important place in education and psychology.

Piaget and other researchers have helped show how object permanence works through a few different experiments.

One of Piaget's first experiments involved hiding toys to see whether a baby would look for the toy. Piaget would show the toy to the baby and then cover it with a blanket.

Babies who looked for the toy showed they understood the toy still existed when they couldn't see it. Babies who seemed upset or confused hadn't yet developed object permanence.

Piaget and other researchers also used the "A not B" experiment to check for object permanence. He would show a baby a toy, then hide it under a box (A). After the baby found the toy under Box A a few times, he would hide the toy instead under a second box (B), making sure the baby could easily reach both boxes.

Babies who looked under Box A for the toy showed they couldn't yet use abstract reasoning skills to understand the toy was in a new place.

Later research helped people realize object permanence could develop before 8 months of age. Researchers worked with babies who were just 5 months old, showing them a screen that moved in an arc.

Once the babies got used to looking at the screen's movement, researchers put a box behind the screen. Then they showed the babies a "possible" event, where the screen reached the box and stopped moving, and an "impossible" event, where the screen kept moving through the space occupied by the box.

The babies tended to look at the impossible event for a longer period of time. This suggests the babies realized:

  • solid objects can't pass through each other
  • objects exist even if they aren't visible

So make no mistake: Your baby is already a little Einstein.

Some signs of object permanence in your baby can be fun and exciting, such as watching them go straight for a toy you hid. Other signs... not as much.

Separation anxiety also tends to develop around the same time as object permanence, and this may be somewhat less exciting. Now your baby knows you still exist whether they can see you or not.

So when they can't see you, they aren't happy, and they'll let you know that right away. So much for peeing in peace.

This can be frustrating at home, and it make it really tough to leave your baby at day care or with a sitter, even when you know they'll be completely fine.

Your baby may also feel less comfortable around strangers at this point ("stranger anxiety"). This can make separation even more difficult — and stressful for you both.

But try not to worry. This stage is temporary, and soon enough you'll be able to leave them safely in their playpen or bouncy chair while you put in a load of laundry or run to the bathroom — without having to brace yourself for that inevitable wail.

Playing with your baby is a great way to help develop their understanding of object permanence. Another benefit? Object permanence games can help your baby get more used to the idea that even though you might go away for a bit, you'll be back soon.

Peekaboo

This classic game is great for your baby, but you can try different things to change it up.

  • Put a small, light blanket (or a clean towel) over your baby's head to see how long it takes them to pull it off.
  • Try covering both your head and baby's head to see if your little one finds you after removing their own blanket. Babies older than 10 months might have more success here!
  • Use one of your baby's toys to play peek-a-boo by popping it up from behind different objects or pieces of furniture. Follow a pattern and see if your baby can begin to predict where the toy will appear next.

Hide and find

  • Let your baby watch you cover a toy with a few layers of towels or soft cloths. Encourage your baby to keep removing layers until they find the toy.
  • For an older baby, try hiding a few toys around the room. Let them watch you and then encourage them to find all the toys.
  • Hide yourself! If your baby can crawl or toddle, step around a corner or behind a door and talk to them, encouraging them to come look for you.

Your baby loves the sound of your voice, so make sure to talk to them throughout the games, encouraging them and cheering them on when they find objects. It also helps to keep talking when you leave the room. This lets them know you're still nearby.

This is a simple wooden toy that can help your baby learn more about object permanence. It has a hole on the top and a tray on one side. It comes with a small ball.

To show your baby how to play with the box, drop the ball in the hole. Get excited and draw attention to the ball when it rolls out into the tray. Repeat this once or twice and then let your baby try!

This toy doesn't merely help with object permanence. It's also great for helping your baby develop their hand-eye coordination and memory skills. Many Montessori schools use it, and you can easily purchase it online to use at home.

If your baby gets upset when you leave the room or quickly grabs for dropped snacks and hidden toys, they're probably starting to get the hang of this object permanence thing.

It's a normal part of cognitive development that helps set your baby up for abstract reasoning and language as well as symbol acquisition.

You might start to see this in your baby when they're just 4 or 5 months old, but don't worry if it takes a little longer. Pretty soon, you won't be able to pull the wool (or super soft 100 percent cotton blanket) over their eyes any longer!