Nipit worked over thumb guards for us
We started with the cheap nail polish – didn’t work. My daughter was four. Then moved to thumb gloves because they look easy – they are and she removed them subconsciously all the time. The went for the most expensive – TGuard – but my daughter switched to her pointer finger! NipIt elbow bands eventually cured my daughter from thumb sucking. After a couple months her teeth naturally went back straight, they are perfect now! Good luck!