Saying "No" to Zion is Tough
Zion is great, but I would probably opt-out of going there on your Denver-based roadtrip. Your kids should enjoy the town of Moab along with Canyonlands and Arches. From Moab, you can go south on US Hwy-191 to US Hwy-491. This drive allows for visits to Wilson Arch, Church Rock and Newspaper Rock. US Hwy-491 (formerly US Hwy-666) takes you through Cortez allowing for a visit to Mesa Verde National Park. In addition to being scenic, this park has lots of easy to get to ruins. When in Pueblo, be sure to do the Riverwalk and the Arkansas River Levee mural.
I have never been there, but your family might enjoy Tiny Town, which is located southwest of Denver on US Hwy-285.