Squash out Thumbsucking
Set up a reward program for when your child keeps his thumb out of his mouth. For example, present him with a sticker for every day that he can go without sucking. Once he's accumulated a set number of stickers, allow him to buy a toy or something special that he will associate with abstaining from thumbsucking. Put a Band-Aid or tape on the tip of the thumb. Reward your child with verbal praise when you notice that the child isn't sucking.