When my daughter was just a few days old she found her thumb. I shoved a soother in and got her to forget about her thumb. My theory was I can make soothers disappear but her thumb will always be there. Very early on I limited soothers to the bed then I cut a slit in all the soothers and she called them broken and stopped liking them. Easily phased them out. The thumb takes a lot of patience and constant intervention by the adults. What are the parents thoughts? There is the bitter nail polish that can be used to break the habit but the parents would have to agree. Otherwise break the habit by interrupting and making him go wash his hands, over and over and over!.