If it was up to them, your kid's room decor would change about as often as their socks, so giving in to their latest whim is a losing (and pricey) battle. Instead of throwing in the towel, pass them the baton by painting their entire room with whiteboard paint. They can decorate however they please-and you always have space to write "clean your room".
Results may vary. Test on an inconspicuous area before use.