AFAIK you don't need a credit card linked to the account, you can get in-store credit from selling the guaranteed drop items from playing a few matches, this is enough to get you started trading.
It's literally "The first hit is free". The sketchy gambling sites spot you bonus skins and stuff for the same reason. It doesn't matter, they don't actually have to ever pay out, so they can just give you fake money to get you addicted.
Unless they're using their own money with the blessing of their parents, this remains in the realm of tin-foil-hat paranoia. There's no reason to believe we're in child gambling crisis because of fake money.