I personally would drive, park at bellagio and take in the buffet, the fountain show and check out the other hotels around there. I was in Vegas in Jan with my 12 year old and we drove (stayed at the Luxor). We were in town for 6 days for the Hanna Montana Concert but we did lots of other stuff.
Other things I can recommend for your family:
Trip up the Eiffel Tower @ night (watch the fountain show from the top, it's great!)
Gondola Ride @ the Venetian
Lion Habitat @ MGM Grand (oh and lunch @ the Rainforest Cafe)
Tournament of Kings show @ Excalibur (1/2 price tickets on the strip)
Titanic Exhibit @ Tropicana
Lance Burton Magic Show
Any Cirque show except for Zumanity
Blue Mna Group @ the Venetian
Stomp Out Loud @ PH
Madame Tussauds Museum @ the Venetian
Have Fun. I just got home yesterday from my 3rd trip in a year, this time just my girlfriends and me, no hubbys or kids