YouTube is what you make of it. There is a huge amount of excellent content for kids. Two examples of channels I'll let my six year old daughter watch just about any time she asks are SciShow Kids and Cosmic Kids Yoga. There are plenty of others, but those are her current favorites.
It's definitely important to curate what kids are watching, but that's true of any medium.
It's definitely important to curate what kids are watching, but that's true of any medium.