Hey Dan,
Here's my chance to possibly "pay you back" for all our great summer. We have been going yearly with kids aged 2-11 on Sunday-Thursday national park trips. Here are some brief ideas. Feel free to pm for more details.
1) Vail / Avon / Beaver Creek - Sunday arrive go for pizza @ Brooklyn Pizza, possibly stop at Mt. Evans on the way or Mary Glacier (personally I got altitude sickness but most dont) or just take it easy on the mountain. Monday Glenwood Caverns (
https://www.glenwoodcaverns.com/park-info/tickets/) half the price of vail mountain with lots more to do and gorgeous drive, kids will love it. Tuesday - drive back out west and go whitewater rafting (we went here -
https://www.raftingcolorado.com/ - we took turns watching the baby as they give you 2 rounds - or get a babysitter) and/or ziplining. On the way back we did the Hanging Lake hike - it's gorgeous but needs a permit now so hurry and get one. Wednesday - we drove all the way to Aspen and did some hikes along the way and had some snow fun in late August. Not sure I'd do the long drive again. Thursday - 2 hour downhill biking of Vail pass. A shuttle will drive you up and you can bike down. Lots of places tell you it's too dangerous to start with the child trailer at the first hour but I'd disagree. Find a place that will let your child come. And then it's time to head back to Denver for lupper at Brooklyn Pizza or elsewhere. Enjoy!
Piney Ranch seems like it might be an interesting place to check out. And there's tons more stuff to add in or swap with Vail as your base camp. Plus chabad has minyanim and food - though grilling your own food will be a lot cheaper.
2) Yellowstone & Grand Teton - will try to write details later.
3) Lake Tahoe (+ Yosemite) - will try to write details later.
4) Glacier National Park (+Idaho) - Don't try to do Glacier with Yellowstone - there just isn't time for both. Stick to one park. Personally we did Glacier over a shabbos - Rabbi Shneur Wolf @ Chabad of the Flathead Valley graciously hosted us for meals. We based ourselves out of the flathead valley - which is only 45-60 minutes from the park. Arrived monday eve. Tuesday did Whitefish Mountain Gondola & Adventure Park (
https://skiwhitefish.com/). Wednesday did going to the sun road (545am early wakeup required plus advance permits). Parked at Logan Pass and did the Hidden Lake hike. Then..... TBC
5) RMNP - will try to write details later.
6) Crater Lake - will try to write details later.
Arizona & Utah are too hot IMHO.
(I'd send you to Kauai - but you dont need my help on that:)