Never mind that paypal has a time-out, even if you left the window open in the browser, it would time out and you'd have to enter the password again to access it. Unless you let your browser save the password which, that's just unsafe, honestly. And that's before even getting into him commissioning a character the account owner owns, and not like, his own character.

(and if your nephew is real and 18 they can get their own Paypal account and bank account and learn some financial responsibility)