Paige had a callous on her thumb by the time she was a week old LOL. She has always been a thumb sucker and still does it now at nearly 2.5 years old. It hasn't affected the way her teeth come through or her speech, and she only sucks her thumb when she goes to sleep, so it isn't like it is always in her mouth. Now she is at the age she is, we have tossed around getting the nail-biting stuff, but we decided not to worry about it yet. For all we know she may grow out of it.