Yeah, it's a sad thing anymore, but when it comes to being sued, you can't possibly have enough coverage. That said, I think if you wanted to let younger players on, you not only would need to have some waivers, you would probably want to get yourself a lawyer to insure that the waiver is up to legal snuff, and have waivers be notarized.
As for insurance, if you have the above mentioned system in place, you probably wouldn't get get any major insurance penalties. If the land had a permanent play use, you could even require a one time safety briefing for everyone and keep those attendance logs on file.
When I was in Seattle some friends and I looked into buying some land for paintballing and private range use, so I have actually done a fair ammount of reading on this. It would be very cool if some folks could kick in for a chunk of land between phoenix and tuscon where permanent or semi-permanent structures could be built and such. Land is so inexpensive here...