J.P.
Hi--
We've taken both my children to a chiropractor since they were newborns. I would start there. Sometimes being born throws the neck out of alignment and if it was never fixed that could explain the neck pain. Most chiropractors are very careful with young children. I can recommend the one we go to (who is actually in the Denver area) and I have friends who use a chiropractor here in Castle Rock that they love. Let me know if you would like some names. You could also try massage. My kids babysitter is actually a massage therapist as well and she's worked on them quite a few times. It doesn't take a lot to work on a child. Their muscles usually respond pretty quickly.
Good luck,
J.