I can't stress safety enough. Most real players who love the game feel the same way. That being said, if you find that you are unable to play paintball with your child, find the person at the feild that stresses safety the most. You know, the one that is always making sure that goggles are on and barrel bags are on even if they are not reffing or playing at the time. ZERO IN ON THAT PERSON!!! Nine times out of ten, he or she is a great person that would actually like to help your child learn the fundamentals of paintball. Nothing, I repeat nothing is more important for a long term love of the sport than being introduced by someone who also loves the game.
As a side effect, paintball is very healthy. I by know means lead a sedintary lifestyle, but a day on the field is more physically challenging than a day at work. So, if your child gets hooked and you find yourself needing to exercise more, grab a rental and go play for a few hours. Beats a treadmill.
PBIF, remember that.