See if you can check out an Unofficial Guide to LV from your local library. It's not worth the purchase for 8 hours, but it's worth looking at for ideas as well as scale.
If it was my family in LV for only part of a day, I'd focus on one section of the strip: South (toward the airport--Excalibur, Mandalay Bay, MGM, Tropicana, Monte Carlo, Luxor), Middle (Bellagio, Paris, Venetian, Caesar's Palace, Mirage, TI) or North (Circus Circus, Stratosphere, Stardust, Riviera). The Strip is a LOOOOOOONG walk from end to end! I'd probably choose the Middle section, since it has the Bellagio fountains, the Eiffel tower, the Mirage's volcano and Siegfried and Roy's Secret Garden (that's the Dolphin exhibit mentioned earlier, plus it has some of S&R's other animals--tigers, elephant, etc).
The other thing I'd look into is afternoon shows. DH and I were there in Sept and saw the Mac King Comedy Magic Show at Harrah's. Totally appropriate for kids and adults and VERY funny and entertaining. His companion act over at the Rio (Ronn Lucas) was amusing, but I felt totally erroneously billed as "family" entertainment. We were glad we didn't have DS along with us.
Again, I say find a copy of the UG to borrow. If you were nearby, I'd let you borrow mine!
Oh, and about the Bellagio fountains, yes they do play seasonal music and yes you can hear the music over at the Paris if you are outside. Consider eating at Mon Ami Gabi in the Paris. It has a patio with Bellagio fountain views and the crepes are TO DIE FOR!

No reservations for the patio, though, so get there early! I can also highly recommend their cream of mushroom soup. Ain't nuthin' like you get from a can, I can tell you that.
Sorry for the length of this post. LV is my other vacation destination of choice! Have a wonderful visit!
D-n-C