I worked for a decade in what I would consider the highest level of our kids' privacy ever designed, at PBS KIDS. This was coming off a startup that attempted to do the same for grownups, but failed because of dirty money.

Every security attempt becomes a facade or veil in time, unless it's nothing. Capture nothing, keep nothing, say nothing. Kids are smart AF and will outlearn you faster than you can think. Don't even try to capture PII ever. Watch the waves and follow their flow, make things for them to learn from but be extremely careful how you let the grownups in, and do it in pairs, never alone.