Is there a way to make games only accessable to specific users (we have kids who don't want others having access to their games) kids being kids, as soon as their backs are turned they are on the other kids games.
There's no way to limit which local accounts can play a specific game aside from parental controls, which sounds like it isn't quite what you want.
That being said, each account on the PS3 should have their own separate save data for each game, and user accounts can't access save data on other user accounts, even on the same PS3. So, aside from arbitrary reasons ("that game belongs to me, you can't have it!"), there's no real downside to letting the other kids play "their" games, and there's no need to worry about one kid messing up another kid's saved game, as long as they're playing on their own account.
Each user account has specific access to the games purchased for that user account. I have an account called "WhitishMink" on which I purchased several PSN games. My other accounts don't have access to those games, because it is a different PSN account (like I can't play Castle Crashers from any other accounts).