And it doesn't need to be the mail room (though that's not a bad thing to have exposure to, perhaps, but circumstances will determine what's appropriate). The most important thing is not to put them in a position that harms[0] the company and that they're not (at least not yet) qualified for. This is not only bad for the company, but for the child, as they are not put a position that allows them to grow, but one in which they can't help but fail in. So it's a failure of parenting.

[0] "Harm" doesn't need to be catastrophic. Misuse of company funds is a kind of theft, and paying someone a salary who is basically on perpetual holiday is unjust, for example.