Forgive me if someone else already posted this. It's a short video and transcript of a Dr. speaking about TN in children. Clilck this link.
http://www.facepain.us/linskey_kids%20and%20TN.html
It happens, but is rare. I know there are parents on this site who have children with it.
There was even a documentary on a couple of years ago about a baby born with it, and the parents would take videos of the baby looking like it was startled, then she would cry and cry. I'm sure it was the shocks and the pain. Then they showed her at 2 years old, and she would just get very quiet, sit very still, and stare at the TV like she was trying to escape her pain through what was on TV. Her way of adapting I guess. I think she was 4 when they did the MVD. It was the first such known case of a person being born with it.