My suggestion would be the Grand Sierra Resort. They have a bowling alley, mini golf,movie theater, bumper cars and a thrill park. It is close to the airport and only a couple of miles from downtown. Reno also has a AAA baseball park featuring the Reno Aces which starts in April. If they are interested in old cars, also visit the National Automobile Museum. Circus Circus is also downtown but not in the greatest location.
Circus Circus was fun for my girls when they stayed there 1 night. DBF's Mom took them camping a few days before he and I could join them (you coulda knocked me over with a feather when she asked if they could with her) and they stayed at CC, they liked it. We like the Silver Legacy a LOT, it's smoke free. And they have $39 room rate offers all the time, I signed up for their emails and I get those weekly just about.