Law/release form for using photos of children on a website?

I’m working on a website for a school that would like to use photos of the school and its students on the website (in a stock photo-ey sort of way, no names etc). Is there any sort of legal documentation on the rules for doing this? For example a release form the parent/student/school needs to sign, etc.

Thank you!

The school should check with their lawyers, the laws would vary from jurisdiction to jurisdiction and I wouldn’t be taking chances with pictures of children.