My daughter, who will be 5 in July, just had another dental appointment this morning and thumb sucking was brought up by the dentist. My daughter has sucked her thumb since she was in utero, and does is mainly when she is going to sleep or self-soothing, so often she's not even aware that she's doing it. He suggested putting a glove on her hand at night, or an ace bandage on her elbow, which will remind her not to suck her thumb. If that doesn't work, at her next appointment, we'll discuss an appliance that goes in her mouth to prevent her from sucking her thumb. The dentist stressed that it was not punitive, but merely to get her to stop sucking her thumb.