Yeah it kinda does?
No it kinda doesn't. Segregation was legal. Women and blacks voting was illegal. Buttlove was illegal. Walking across a street that's empty for miles across is still illegal.
Now obviously segregation was immoral, women and blacks voting is moral, buttlove is moral and so is walking across an empty street. Clearly this logic is flawed. I don't even have to give these specific counterexamples, but this more general one:
In country A, action X is legal. In country B, action X is illegal. If legality determined morality, then action X would be 100% immoral and 100% moral at the same time. That's impossible, so we have a contradiction. That means that legality does not imply morality.
Now, in
many cases it is the case that things that are legal are moral, and that things that are illegal are immoral, but that's not always the case, which is why you can't use it in an argument. Which is basically another way of saying that any logic that permits a single counterexample is invalid.
This means you have to base your argument off something other than legality. If you seriously can't think of an argument against child enthusiasm other than "it's illegal" I fear for your critical thinking skills. (Sorry if this is late but it still needs to be said)