My kids LOVE going to the Adventuredome inside Circus Circus every time we're in Vegas. They are 8 and 5 years old and they could literally spend ALL day here without getting tired. We always get the wristband, otherwise it could get really expensive. They offer so many rides, carnival games, video games and short 4-D movies.
As I mom I'm glad we have found an indoor theme park, but I'm not 100% happy with the cleanliness of the place and some of the rides have seen better days, but my kids seem to be enjoying themselves, so I try to set all my concerns aside and let them have fun.
Also, it gets very busy here on holidays and weekends and other kids tend to be rude and cut lines so just make sure you to keep an eye out for your kids, especially the little ones.