I have two kids living in my household (5 and 10) and my daughter (8) coming over every other weekend. I setup up everything with two factor auth. and just use a prepaid Visa card for everything online so I only have disposable money to use for stuff like that.
That said, accidents with kids happen very often and when you become parents, it's not your first thing in mind to activate 2fa on your consoles and tablets and whatnot. And when they are old enough to actually play some games here and there you can quickly forget about something like that and while it may not be enough money to bankrupt someone,it can surely put a dent in short term stuff. Buying clothes, car repairs, home repairs etc that also can snowball a bit and can hurt. Just because someone hadn't had their eyes 24/7 on the kid or wasn't able to afford a nanny to go to the toilet or something.
2FA shouldn't be opt in but mandatory imo! Or a spending limit that you have to recertify when you get over. It should not be the standard option that you can spend without limits and destroy your short and maybe longterm future by an accident.