It's tough, Vegas isn't really a kid friendly place. Circus Circus does have plenty for kids, but it is run down and it is way too crowded, I would not stay there.
Unless you plan of letting the kids run free, you have to be around your kids anyways. So, I would say just stay near the M&M world/Coca Cola world (MGM, NYNY, Excalibur) or Fashion Show mall (Mirage, Wynn, Venetian). At least at those places, it is clean. The M&M world area is under construction right now though and not as kid safe. I would opt to be near the mall area.