Can parents close their child's Facebook account?

[CTyankee]

My granddaughter, age 12, has always been a good student until the past 6 months or so. She is not doing homework, or doing it poorly, and her grades have slipped badly. All she wants to do is go on Facebook and other distractions.

Surely, there is some way a parent can just yank the Facebook away if, after repeated tries to have her do homework, and do it well, before she goes on Facebook. That hasn't worked.

Children are not allowed to buy cigarettes or drink in bars...so...