Circus Circus, Stratosphere, Sahara, Aladdin are all good value conscious and family-friendly hotels in Las Vegas. I think Circus Circus would be the best choice and most suitable for kids. If you may want a nicer hotel for your money, find one off the strip without a casino in it. You can still plan trips to the family activities and enjoy cleaner and better accomodations at night.
My friend, Anthony Curtis, is a great
resource for family friendly activities in Las Vegas Other resources for kids activities In Las Vegas: Posting at kidsinvegas.com