A minors bank account on hold for documents????

Why would a minor childs bank account (linked to mine) be on hold for documents????????? Hence the fact that she is a minor. Her birthday money was paid into her account and she wanted to buy herself something and the card declined!!!!!!!! Why? And no one can say what the problem is and what exact documents they need. Only a message saying that a number must be called. And we all know how that episode goes, call centre, press 1 for this and that...2 for whatever and holding on. This is not on! A minor?