Don't tell those parents about free-to-play games! Those are 100% legal and more dangerous and expensive than gambling can be. Oh wait, they only get video game money from you, the parent, and you say no, so that's not an issue. Wait, where are the kids going to get their gambling money? Right, from you, the parent. If you are worried about when they turn 16, get a car and a job, and start making their own, guess what? It's illegal for them to gamble so the entire argument is invalid. How can you make protecting children a defense of any law regarding something that is illegal for children to do in the first place? That's WHY it's illegal for children.
If I am tasked to make something illegal I'm not even going to make a cohesive argument. Say I become a senator (something I have no interest in, but for the sake of argument) and I want to ban fanny packs. I'll stand up there on the stand and say, "Children", and step down.
On a more serious note, if see your child wearing a fanny pack you can expect him to be beaten mercilessly by his peers. Hence, "children". Let's ban fanny packs!