> Any actual reasons or are we limiting them just because?

Just because they aren’t ready to make informed decisions, yes. If they were ready, they’d be called adults.

> My parents were sure that sitting too close to a TV ruined your eyesight. Should we get a law that forces people to sit at least X meters from the TV?

It is children’s freedoms that ought to be restricted. Not their parents’. If you don’t understand the difference, that’s a problem.