We had three nights in Vegas with our girls aged 9 and 6 and we all loved it.
We spent an entire day walking down "the Strip" and still didn't see everything.
We saw the Bellaggio fountains, the lions in MGM, tigers in Mirage and Volcano and the Gondolas at Venice, and the only thing we paid for was lunch and a ride on the Gondola (but we could see it for free).
We found people promoting the "adult" entertainment stayed away from us, and only approached me (dad) when I strayed too far from them, so I don't think you should be too worried about this.
We used our second day to take a tour to the Grand Canyon - you can take all day bus trips (which are about $60 but require 12 hours on a bus) or fly/bus trips.
But our kids thought the best thing was the buffet at Bellaggio - they loved being able to choose dozens of things to eat, and to keep going back. We went at lunch (which is cheaper than dinner), but got there late and stayed until 3, so that filled us all up until well into the night.
(Lucy, 6, rated the buffet the second best thing she did in America after Disneyland!)
We stayed at Luxor - (the pyramid) but found it a bit shabby, and a bit too far away - it also had a pool that was not very kid friendly.
Read our trip report on our day in Las Vegas here -
http://www.ballofdirt.com/entries/5333/36755.html
Or check out
www.cheapovegas.com for reviews of hotels, buffets, pools and free things in Vegas.