There are basic skills that everyone needs, for example, the three R's: reading-riting-rithmetic.

There is shared knowledge and history that form the foundation of a culture.

There are basic life-skills, like understanding banking, the local political system, etc.

On top of all that: knowing how to think and reason, knowing how to find knowledge and learn new things.

So many parents are apparently incapable of covering these basics. In particular, many parents who home-school or, worse, unschool lack many of these capabilities themselves.