I would advise getting as many people as possible per car, and getting there early to stake out a spot. I grew up in Eastern Washington, and my friends and I usually have a huge campsite, which is all the more fun.
I would say that it is not really younger-kid friendly. The campsite is usually pretty full of drunkos, and there is generally someone playing music loudly all night. I always feel sorry for the parents who have young kids trying to find a place to relax inside, because it has been really hot, and there is no re-entry. And, as a concert-goer, I wish people would just wait a few years and save their kids' hearing.