Hello A., my name is C., and I am a stay at home mother of 5 children under the age of 5. I have a four year old daughter that is a major thumb sucker, so I know exactly how you feel. My pediatrician always tells me that you have to be persistant about removing thier thumb from thier mouth and saying WE don't do that, so that they know as adults and people in general, we don't suck our thumbs. Also, I spoke with my children's dentists about the effects on thier teeth from thumb sucking because I thought my daughter already has damage from thumb sucking, he told me that they usually don't worry about thumb sucking damaging thier teeth until they start to get thier permanent teeth in. I have been trying for over two years to discourage my daughter from sucking her thumb, but no matter what I do or say, she still does it, that is her security, just like my other daughter, she sucks on her blankie and that is her security, I think they all have something that makes them feel secure, it's just that we as parents may not like the security they choose. All I can say is be persistent about letting her know that WE don't do that and pull her thumb out of her mouth and try not to get discouraged by it.