Three and six year olds? If you want them to see "Stomp," take them instead to shows at a local high school, middle school or dance school that is doing a hip-hop or modern dance recital! Much cheaper and at three and six, frankly, your kids won't know they didn't see "Stomp" (except there likely will be no garbage can lids used for percussion....)
For cost-friendly, kid-friendly performances, dont' look just to professional troupes but turn to your many local dance schools of all types, local drama schools, high school drama departments, local children's theatres (either performances BY children or by adults FOR children) -- they are all out there and are much less expensive than going to "professional" stage shows. Also, when you attend these shows, your money is going to help that school or non-profit local kids' theatre -- and it's much needed at all of them. These groups are very tolerant of kids who might have to be taken out for a time or who have shorter attention spans. If it's dance you want to show your kids, there are surely many, many dance schools in Colorado Springs doing performances all through the year that are open to the public.
As for dress rehearsals, yes, do call and ask, but don't be surprised if some or even most places say no. They do often reserve the dress rehearsals for invited audiences of family, friends or patrons, or keep rehearsals closed because frankly the big, successful shows know they can fill every seat at full price in the regular performances. Meanwhile, do try local and school dance and theatre -- you will be amazed at how good the performances are!!
Take your kids to everything you can -- LIVE performing arts are terrific for kids. My daughter has gone to lots of plays, concerts, and dance shows since she was about two, and now dances five D. a week and is in rehearsals for her sixth "Nutcracker." While it doesn't always create a dancer or actor, seeing live shows does teach a child to appreciate the arts so very much and gives them great pleasure -- and it's far better than TV or movies!