> Enforcing limits on students is the job of parents
Luckily in California we understand the value of protecting kids over uninformed adults. That's why we require vaccines to attend school.
Oh, but they most certainly can. See the aforementioned vaccine laws. Or the law that provides free breakfast and lunch to every California student regardless of income. Of the law that requires dental coverage for anyone in the state under 18 (and provides it to those who can't afford it).
No matter how bad your parent is about feeding you, at least you know you'll get breakfast and lunch every school day, and you can get your teeth checked.
There are many laws that protect against poor parenting.