It is more difficult to control thumb sucking when the child is asleep, because the child is unaware of this involuntary action. So, try this habit-breaking technique that is usually successful within two weeks. Before your child goes to bed, wrap a 2-inch wide ace bandage lightly around their fully extended arm [straight]. Start about 3 inches from their armpit and continue down past the elbow. This will not prevent your child from putting their thumb into their mouth. However, as soon as they fall asleep, the tension created by bending the elbow will pull the thumb from their mouth.