You can monitor and restrict Steam usage with parental controls. This is no more unfeasible than WiFi and device time limits, and last I checked, children don't carry a credit card. What's the mystery here? An 8 year old is not accruing bitcoin to buy skins.
Meanwhile you have users here that will tell you that refusing to give their kids smartphone or even any video game is not that hard, but it seems needsly restrictive.
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.
Meanwhile you have users here that will tell you that refusing to give their kids smartphone or even any video game is not that hard, but it seems needsly restrictive.