I have some friends who are parents. They sometimes loan their (very young) kid a tablet to keep him distracted while they're busy. It keeps him from causing problems for himself.

The kid goes to Youtube and only watches vacuum-cleaning videos. For hours.

He also believes every TV is (or should ideally be) touchscreen interactable. He likes boping the people on the news. He thinks they're puppets.

He's a healthy, normal kid. What I'm trying to express is that we don't know how normal kids react to Youtube and its effect on them. It can be surprising.