Babies track the frequency and co-occurrence of features in their sensory input, using the statistical regularities of what they hear and see to carve the world into categories before they understand meaning. For example, infants detect which sound sequences recur in speech to isolate word boundaries from an otherwise continuous stream.
Children build cognitive understanding partly through bodily interaction with their environment, not through passive observation alone. Motor milestones such as reaching, crawling, and manipulating objects supply the experiences from which spatial and causal concepts are constructed.
Around age four, children become able to attribute to another person a belief that differs from reality and from their own knowledge, demonstrated when they predict a character will search where he left an object rather than where it was secretly moved. Younger children fail this because they cannot yet represent that others hold mental states distinct from the true state of the world.
Children learn language through interactive exchange with responsive partners, not from passive exposure such as audio or video alone. The back-and-forth of joint attention, where child and caregiver focus on the same object while it is named, supplies the referential grounding that mere sound input cannot.
Viewing children as little scientists reframes their errors and play as experiments: they form hypotheses about how the world works, test them, and revise their mental models in response to outcomes. What looks like a mistake is often evidence of an underlying theory being probed rather than a failure of memory or attention.
Rather than advancing through uniform stage-wide leaps, children develop competence unevenly across different domains, acquiring skills piecemeal and showing understanding earlier under simplified task conditions. A child may reason maturely in one area while remaining immature in another, so performance depends heavily on how a task is presented.