Frankly, I don't believe a law should be passed making it illegal for minors to go on Facebook. There's too many laws as it is. Facebook need to change their policy. Right now, I believe it is set at 13 and above with parental consent (a questionable method).
The best thing for a parent to do is to not put a computer in a child's bedroom where it cannot be supervised 24/7. Not even these softwares where parents can set up limited internet access because they aren't foolproof.
Also, the parents should always look at their child's profile on a daily basis and ensure that they are not given limited profiles.