I don't know what you'd want to do in Vegas with that age group. If you walk down the strip, people hand you cards with pictures of naked women that have numbers you can call if you want a private strip show. I don't think I've ever walk anywhere on the strip without seeing that. There's lot of other stuff going on that I wouldn't want small children near, but that gives you an idea.
That being said, there are things that kids can do. Circus Circus has some type of indoor amusement for kids (I've never been) and there's a roller coaster on top of one of the hotels. There are shopping malls, but wherever you go, there are a lot of very drunk people. You absolutely will be in an elevator with a drunk person putting their face in your kid's face telling them that they are so cute.
If you stay away from the strip, there's some really nice hiking (July will be miserably hot) and some other interesting things that you can drive to. I think it would all be extremely boring for kids, but it can be nice for the adults.