Some excellent suggestions, not a lot to improve on, other than to suggest you forego Rocky Mountain National Park this trip. In August, it is an absolute zoo for the entire month, weekends and weekdays. Park personnel are looking at ways to manage traffic better, but there's no short term solution. And...it's really not in keeping with your "theme" of the southern Utah NPs.
I would suggest adding in place of Rocky, Mesa Verde NP and Great Sand Dunes National Park and Preserve. In Mesa Verde, there's gonna be a lot of kid friendly things to see and do, and if you can get reservations inside the park at Morefield CG, even better. As for the Great Sand Dunes, again, kid friendly, they will love the dunes and Medano Creek that runs at the base of the dunes. There's a CG in the park as well as a state Park (San Luis SP) outside the park, and close by.