We don't have an accurate history of every society that has ever existed, so your claim is unverifiable. Don't make impossible to verify claims.

I wouldn't say a system supports child labor if it's outlawed and heavily punished. In the same way that I'd say a system doesn't support murder if it's outlawed and heavily punished. Sure, every society we know of has had murderers, and child laborers might exist in the same capacity in most societies, even if they're outlawed, but it's not supported by said system.

Also, my claim was that a system exists where child labor isn't allowed. Even if that system has never been put into practice (it definitely has, but just for the sake of argument), it's obviously true. Maybe you're unconcerned with hypothetical systems, and you're absolutely convinced that the only practical systems that can exist are ones where we rely on the labor of children to succeed. You'd be a fool if you believe that, but I understand some people are foolish.