Roblox spending spree

UPDATE: My 12yo spent $47 on Robux without asking me. FORTY SEVEN DOLLARS. On virtual currency for a game. I had my card saved to his account for "emergencies" which apparently includes limited-time avatar skins.

I've now removed the card, turned on purchase restrictions, and he's doing chores to pay me back. But I'm genuinely curious - how do you guys handle this? Do you let them have ANY spending capability or is it a hard no?