NASCAR Cafe (like a museum inside and there is some kind of roller coaster ride that leaves from there)
Harley Davidson Cafe (motorcycles move on chains over your head while you eat, and you can sit on one to get your picture taken)
Showcase Mall: M&M World, Coca Cola (you can go inside the huge bottle) and Gameworks
IMAX Theater (I think at the Luxor)
King Tut's Tomb (at the Luxor)
Obelisk Ride (at the Luxor)
Hard Rock Cafe
Cheesecake Factory
Secret Garden and Dolphin Habitat at the Mirage
Madame Tussaud's Interactive Wax Collection
rides at Excalibur
Chocolate Factory tour (at Henderson)
Lake Mead (they have an ATV tour that I think you qualify for age-wise and there are jet ski rentals)
And please do the light show at Fremont Street as everyone recommended. You can get a day-pass for the bus that will pick you up on the Strip and take you down there and bring you back. It's about $5 for the whole day, I think, very cheap, and you can ride as many times as you want.
They were building a monorail last time I was there, too, that runs from Mandalay Bay to the other end of the Strip. I think it was supposed to be finished last year. That would be a good way to see everything and get your bearings. You can always go back to the stuff you want to see.
The Treasure Island pirate show is excellent (very crowded - get there early to get a good place to stand to see the show). The fountains at the Belagio are excellent (but they don't run if it's very windy).
Also, check and see if there are any concerts in town during your stay. My friend from Houston and I saw George Strait at the MGM Grand last time we were there (they have a fantastic Arena that is great for concerts).
The Wayne Newton show at the S ust is well worth the money; I had never cared for Wayne Newton until I saw him live at the Laurie Auditorium years ago. He does a great live show and is outstanding at home in his own theater at the S ust. I don't know what the age restrictions for his show are, but worth checking out.
There's plenty for under-18s to see and do in Vegas. You just have to look around for it.
Check out that bus! It's cheap and takes you anywhere on the Strip you want to go or all the way downtown to Fremont Street. And, they run every few minutes, every 10 minutes or so (just don't be shocked at anything you might see on the bus, we have seen some really freaky folks on the bus,

). And check out the monorail, too! I don't have any idea what they charge to ride the monorail but I am really looking forward to checking it out on my next trip.