My family and I went every couple years when I was younger. I guess I can only give you a kid-friendly perspective...I haven't been since I was about 12. The highlight of the kid's lives was going to Circus Circus to play all the carnival games. Your son will be able to spend hours in there, but be warned - you'll come back with a ridiculous amount of stuffed animals.
Other than that, Treasure Island used to put on a cool, free pirate show - not sure if they still do that. The Bellagio? Maybe? Has a water show that's set to music. Excalibur has a Medieval Times-esque dinner show where knights joust. I went to Medieval Times last year and loved it as an adult and as a kid, so if it's similar, it'd be a great choice for both you and your son.
The adults always dragged all us kids around to look at the different hotels and architectures - we always hit Caesar's Palace without fail. I'd like to do that now that I have an appreciation for that kind of thing. Also, the Mirage has a white tiger/white lion/dolphin sanctuary that I've never been to, but it looks neat.