Object Permanence: The understanding that objects continue to exist even when they cannot be seen or heard. For example, knowing that a toy still exists even if it is hidden under a blanket.
Conservation: The principle that quantity remains the same despite changes in appearance. This relates to hiding objects because even though you can't see the toy anymore, its quantity does not change - it's still there.
Egocentrism: The tendency for young children to only consider their own perspective and struggle to understand others' viewpoints. This can affect how toddlers search for hidden toys because they may forget that someone else knows where the toy was placed.