Object permanence is the understanding that people and objects remain present even when they cannot be seen.

Babies will begin to show they understand this by knowing you are still there even when they cannot see or hear you.

Cause-and-effect is understanding that something is occurring due to an action.

A baby may show that they understand cause-and-effect by kicking a toy to intentionally knock it down.

Problem solving may be demonstrated by their understanding of how they can "get something".

Babies will start to demonstrate problem-solving by turning their heads to see where a sound is coming from and by reaching for things they want.