I did about four years of customizing paintball guns for a living- the shop that later became KAPP was where I worked. I was airsmith to the Ironmen for a season as well.
I'd suggest buying clean used WGP Snipers, or WGP Autocockers that have been converted back to pumps. You can pick up one with a premium barrel for under $200.00. Here's why- they are incredibly heavy duty and reliable- you'll spend less time fixing and more time playing. They are incredibly accurate with a good quality DYE or J&J barrel- mine would hit a knot in a piece of 3/4" rope at a measured 25 yards (Bill Wing of DYE and I spent about 10 minutes shooting that piece of hanging rope one day at our field in Nor Cal). A pump will use less paint and air, so you and your kids will spend less, and play more. Affordability is an issue with paintball.
Learn to play "hopperball". Don't bring leaders or fanny packs onto the field, just play with a stock 90 or 150 round feeder only. Conserve and look for angles. Keeps things simple and makes a case of paint last all day.
I'd head over to M Carter Brown, which is a vintage paintball marker website. Read the forum and you'll get an idea of what works and what doesn't. PM me if you have some specific questions.
The Tippmann guns are a great value, by the way. I have a friend who has an SL-68 (not the II) and it still works, and shoots great. The Tippmanns reaaly focused on building a reliable, heavy-duty product. Certainly not flashy, but they always work.
Clean your barrels between games with rubbing alcohol. Buy good quality paint- you'll thank me later. Buy the best quality eye protection you can and take care of your lenses. Check out a real field and follow the safety procedures (barrel plugs or sock, chrono before every game, no turning up the velocity on the field, no overshooting, etc). Paintball is a very safe game played right.