Good points made by all.
I also agree with the attention paid to safety. As a parent, I teach my son safety, so should you. On the flip side, I have several families that play on my team. Fathers and sons, Fathers and daughters, husbands and wives. It is a great way to spend time together and work out grudges...
During a recent large game I played in, I found myself yelling at several kids to keep their masks on. I explained to them why it was so important and that it wasn't personal, they seemed to understand. Eyes can't be replaced...yet. Don't get me started on barrel blocking devices (plugs or condoms).
Don't shoot for the moon on that first marker, but don't skimp too much either. I started with a Brass Eagle Eradicator that was worthless and came with a cheap mask. I would spend a little more, get a Tippman 98C and a mask with a good lens and wide range of vision. Get a barrel condom, they're acceptable everywhere. Teach yourself proper care of the equipment and pass it on to your kids.
If you don't want to play, hang out. All too often have I seen the mini-vans and SUVs drop off a couple kids and drive off. Get a good book and a comfy camp chair, hang out by the car and wait for them to come off the field. Every parent knows that glint in the eye when a child gets to share an exciting event with you, especially if it just happened. Give them a Gatorade and listen to their play by play.
Don't fight their battles every time. If there is a problem with a player, teach them how to handle it properly - ref, owner however. I don't mean don't get involved EVER, but pick your battles. If the child can't deal properly, how will you be able to leave them to play on their own? Sportsmanship. Far too often today poor sportsman are spoiling a great game for the people out to have F-U-N fun.
Shameless plug for my friend - Scenario Paintball Book
A good book for the player starting out, or in my case the player who wants to be better.