When did schools suddenly become "in loco parentis"?

Friend went up to see the principal and the principal said the school and it's personnel are "in loco parentis" and my friend said "I don't remember giving you that permission" and the principal said something about it being the law.

Cause they won't even let you take an aspirin in school unless it is administered by the school nurse accompanies by a doctor's note. A friend signs her kid out of school to give medication and then signs the kid back into school cause she doesn't want them knowing her family business. So, how come they can give sunscreen? And, if sunscreen, what else will they administer? I mean if you tried to put sunscreen on the teacher, that would be assault.