Having a car is a must for your purposes, so we're glad you're renting one, and sorry this response is coming a little late (we'll send it to you personally, in case you're not online while you're here).
While it's a much-repeated cliche that Las Vegas long-ago abandoned its ill-conceived idea to become some kind of Disneyworld, the city is now home to a growing population of child-bearing residents and still wants to accommodate those visitors who bring little ones, even though we recognize that this is not Sin City's raison d'ĂȘtre. So, here are some suggestions of things that might be fun for your whole family to do, with a mini-review of the Discovery Children's Museum, since an LVA staffer just took her 6-year-old daughter there and had a blast:
Review: Recently, I took my daughter to the Discovery Museum for her sixth birthday, and I have to say that it was probably the best $24 ($12 for each of us) I ever spent. There were so many things for kids to do, from hands-on projects, to imaginary play, to arts and crafts. This place has something for all ages and although we didn't go into Toddler Town, which is what you would most be interested in, we did visit every other section of this four-story museum.
"Besides the giant play structure that runs through the middle of the building, my daughter's favorite space was the 'Working Area.' They have a pretend grocery store with isles of food, a deli station, a meat station, and cash register, etc., a veterinary hospital where the children can pretend to X-ray animals, take temperatures, give medicine, etc., a bank, an oil shop, a restaurant, and a construction zone -- complete with hard hats and bright vests for the kids to wear. It's really imaginative and interactive and fun!
"We spent about three hours here and we could stayed all day, if we didn't have other things to do. I highly recommend.
"Just a few extra useful parental pointers: When I went outside for a break, there were lots of people coming and going; you know it's a good place when all the kids that were leaving were crying because they didn't want to leave! Note that there is no food or drinks allowed, however, so make sure you eat before you go. They have an area at the entrance where you can buy drinks from a vending machine but that's it."