My son battled cancer from the age of 3mos to almost 2 yrs old. He survived the very harsh treatment and contnues to saty healthy. His biggest comfort coming out of surgeries and all the treatment was his thumb, even the doc always made sure it was always uncovered. He still does it but he lacks no maturity the chemo rotted his teeth anyway and I think when he is ready he will just stop. Just too many other things to worry about