What state in america is the parents liable for a minor till the age of 21 years old?

What state in america is the parents liable for a minor till the age of 21 years old?
Depends on the situation. It would be best to ask an attorney for the state you are inquiring about because all the laws change.

What do you mean as liable ?

A parent is liable for child support to the custodial parent often to 21 if the child is still in college.

But at 18 a child is a adult in all US states and the parents are no longer liable for the child's legal liabilities.

None that I know of, unless the child has special needs or is a student at a post-secondary educational institution.

Umm at 18 unless they are handicap then at 18 they are considered an adult and the parents aren't liable