>why can't we just leave all responsibility to the parents?

because we don't live in a 15th century peasant village. The average adult reads at a 7th grade level, 20% of adults are considered functionally illiterate, most adults can't navigate digital spaces, privacy and social media themselves or take on trillion dollar companies.

This also hasn't applied in the offline world since idk, Kant and Hegel, every modern state recognizes that children are persons and citizens in development, not private possessions. If your children have broken bones you can't explain or your parenting is considered to threaten the welfare of your child you can be pretty sure you'll have the authorities at your door quickly, and countries like France have given children the right to sue their parents in case they breach their digital privacy. So called 'sharenting' laws exist because it's not guaranteed that parents are even respecting the privacy of their own children.

> If your children have broken bones you can't explain [..]

I don't mean to be combative about this but

1) do you have children and 2) if yes, how many times have you taken your child to hospital with a broken bone

I have (unfortunately) got a certain amount of experience with this, and I'm not sure it works the way the uninitiated may think it does.

Your sharents don't love you like your parents do.