J.F.
I don't agree with the person who said to teach them to suck on their fingers. I've known kids that I grew up with that continued to do it (i'm talking about into adulthood) You can't take away a finger or hand when they get older like you can a pacifier. Thumb sucking is a bad habit like nail biting or hair pulling etc. Don't encourage something like that. Just work on the muscles in their mouths like the other lady said.