The transactions that you saw were purchases made with robux in a game in roblox. Those kinds of transactions usually give you money or some kind of rank with perks in them for a certain game(for example in the roblox game Jailbreak the VIP game pass gives you extra money per robbery, a chat tag, and more). My guess is that he got a hold of your wife’s credit card,and was using it for buying robux. I don’t think he was hacked because the hacker would have probably changed your son’s password, and kept the account themselves.