The Denver Auto Show is April 7-11. My family and I went to this last year and it was really fun. It's at the Colorado Convention Center. Here is the description:
"The Denver Auto Show is bigger and better than ever! The car show is the perfect place to see the latest examples of fuel efficient technologies and aftermarket accessories. At the Colorado Convention Center you'll not only see all the new 2010 models, but also be treated to sneak peeks of selected 2011 intros, concepts and the latest in tricked out cars!"
This is really fun for the whole family. There is a kids pit stop that has a HUGE inflatable fire truck slide, and this year there is balloon artist and yo-yo master. There are also tons of food/drink/snack booths set up.
*Click HERE to get more information
*I HIGHLY recommend taking the light rail, it is a lot cheaper than parking downtown, and it goes right up to the Colorado Convention Center, plus the kids love it!