I used to be anail biter too but since getting acrylic nails, I stopped. When I had the nails taken off, I never went back to the habit but they did always seem to break *grrr* Now, I have the acrylic nails again for a little while.
About children, very good question bjb! My 2 year old bites her nails all the time and her toe nails too!!! I have no idea why or how this started, she's been doing it for a year. Any ideas how to get her to stop?