I understand why you’d find this frustrating, but I think parents should have the freedom to buy their kids whatever toys they wish, and wanting them to clear it with you first seems like a bit of an overstep to me, particularly if the child asked for it for Christmas. In general, what parents buy their kids is a highly personal thing. Will it make sessions tougher? Yes, but you can get creative and find other ways to motivate this client. Satiation, IME, often happens regardless of whether or not parents give their child access to the same reinforcer anyway...this was just a bit of a catalyst to the inevitable. You can always ask your supervisor for alternative suggestions if you’re struggling to come up with ideas on how to motivate this client. Good luck OP!