Lead
You hand a child the tablet. Ten minutes later you glance over: they are watching a channel you have never seen. You started them on a toy-review video; somehow they have migrated to unboxing videos from a stranger. This is not an accident, and it is not the child's mistake. It is a designed outcome.
Understanding how YouTube's recommendation engine works is a prerequisite for doing anything about it. Without that, "they're watching too much" is a feeling — not an actionable diagnosis.