Denver to Las Vegas Travel Advice 6 days in July

[vcrodriguez2001]

I am planning a road trip for my 9 year old son and me following a convention in Denver. I'd like to take 6 days (or so) and end up in Las Vegas. I'm aware that the straight route can be driven in one day (750 miles or so). My tentative plan looks something like this (and I'd like a bit of feedback on what can be reasonably added or can't be missed. I'm not opposed to leaving the interstate, but just need safe arrangements since I'm a single mom with just one child.)

From Denver to Colorado Springs to see Garden of the Gods and Pike's Peak (I visited both when I was pregnant with him, so these are a must do on the list). After that, these are the things we'd like to see/do: Navajo Nation, Zion National Park, Bryce Canyon and a visit to Best Friends Animal Society Sanctuary(Kanab, UT) to volunteer for 2 days at least, Joshua Tree/Mojave (I'm not sure how far this actually is from Las Vegas). We are using Vegas as our ending point because of the less expensive accommodations and flights in the summer months.

Are there other sights along the way that we should definitely drive through, not miss, etc? We are both "outdoor-sy" and would like the opportunity to hike a bit and not just see our nation's beauty through our car windows.