Hide the brick: why object permanence is the cognitive leap that changes everything
When your toddler searches for a hidden brick, they're demonstrating one of the most significant cognitive milestones of infancy — and you can build on it deliberately.
Before about eight months, if you hide a toy under a cloth, most infants will stop reaching for it. Not because they're giving up — but because, as far as their brain is concerned, the toy no longer exists.
This is the world before object permanence: the understanding that objects continue to exist even when out of sight.
Piaget described acquiring object permanence as one of the central achievements of the sensorimotor stage. And the moment a child searches for a hidden object — not just glances around, but actively looks — marks its arrival.
Why it matters beyond peek-a-boo
Object permanence is often discussed in terms of attachment: children become anxious about caregivers leaving because they now know the caregiver exists when absent. That's real. But the cognitive implications go further.
The ability to hold a mental representation of something not currently visible is the foundation of:
- Working memory — holding an idea in mind while acting on it
- Symbolic thinking — the precursor to language and abstract thought
- Cause-and-effect reasoning — connecting an action now to an outcome that will appear
In other words, it's not just a milestone to check off. It's the moment the child's mind begins to represent an internal model of the world.
Using bricks deliberately
Bricks have a property that makes them excellent tools for object permanence play: they stack and hide naturally.
A DUPLO brick under a small box, inside a cup, or covered by another larger brick creates a controlled hiding event. Unlike a toy under a cloth — which toddlers eventually learn to sweep aside in one gross motor move — bricks require more specific interaction.
Try these progressions:
Simple hide (8–12 months): Place a favourite small brick under a cup while the child watches. Pause. Do they reach for the cup? This tests basic object permanence.
Displacement hide (12–18 months): Hide the brick under cup A while they watch, then move it to cup B while they watch. A child who has only partial object permanence will still reach for cup A — where they last saw it placed. A child with stronger object permanence tracks the displacement.
Invisible displacement (18–24 months): Hide a brick in your closed hand, then place your hand under a cup and leave the brick there, withdrawing an empty fist. "Where's the brick?" A child who passes this is representing a sequence of invisible events — a significant leap.
The A-not-B error
Piaget documented a fascinating phenomenon: infants who have successfully retrieved a hidden object from location A will continue reaching toward A even after watching you move it to location B.
This is called the A-not-B error, and it persists until around 12 months. It tells us something important: early object permanence isn't just about the object — it's partially about the action that retrieved it. The motor memory of reaching to A overwrites the updated perceptual information.
This error disappears as the prefrontal cortex matures and working memory strengthens. Watching your child stop making this error — start tracking to B — is observing neural development in real time.
Hiding games are one of the few play contexts where you can directly observe a cognitive milestone as it develops, and gently practice it. No toys required. A brick, a cup, and a watching child is enough.