Those are students, presumably with parental guidance, signing documents for their education.
Again, attorney here: whether a minor has the legal capacity to sign a contract is largely a matter of state law, so it can vary, but generally speaking, a minor lacks the legal capacity to sign a contract, except for those concerning food, lodging, or clothing, if the minor is over the age of 16. So the determination would be on a case by case basis, and if the person can show that the contract was coercive or signed under duress (probably not hard here) the contract could be declared void no matter how old the person was at the time of execution.
Here is a pretty good explainer: http://www.nolo.com/legal-encyclopedia/lack-capacity-to-contract-32647.html