I tried to research on what platforms allow kids to buy stuffs online, but I always get that result about they are not allowed to buy online since what has been said they are minors. So I think law won't allow them to do that to avoid getting any issues towards bad spending's or other uncontrollable matters.
Every platform that officially does not allow children to buy goods is actually in compliance with applicable laws, and children are still under parental supervision so they cannot do that, so no platform allows it.
Maybe they can do it thru p2p if there's an online seller would allow to get paid on crypto in exchange with their toys or other things kids needs.
Hmm maybe it can be done with P2P --- it's just that children rarely do P2P transactions with strangers, if only to buy toys, just go to the store with parents.