If the Rockies are in town, you can catch the bus from Boulder to Union Station in Downtown Denver. You can take in downtown Denver and walk over to a baseball ball game at Coors Field in LoDo. If your kids have never seen a middle reliever give up a 5 run lead in one inning, this would be a great opportunity for them to see one. The Downtown Aquarium is near there too.... probably too a bit too far to walk, but a 5 min Uber ride.
In Boulder, catch a happy hour/dinner on the patio at the Chataqua Dining hall (see Nitzilla's earlier post about Chataqua Park). Restaurant sits by the park, so kids can play at the park, whilst mom and dad have a glass of wine and watch the sun come down. Pearl Street Mall is a hit, esp on weekend nights in summers.
When in Estes, check out the Stanley Hotel ghost tours.... Note: if it's possible to avoid Estes on the weekend, I would for sure. Also, +1 on whoever mentioned the Peak to Peak highway drive out of Estes. It's beautiful.
If you don't have a place lined up in Colo Springs, Cheyenne Mountain resort has a great set-up for kids. Ours loved it when they were that age. Don't know if the trick still works, but we used to use Hotwire and specify we wanted a 4-star hotel in the region its located (you'll have to do some Google mapping to sort it out). Given how Hotwire gerrymandered their Colo Springs map, it ends up being the only 4 star hotel in that section. So we'd get killer deals and know the "hidden name" of the resort was going to be Cheyenne Mountain. (That was 4-5 years ago. Not sure if still works. YMMV)
Finally, if you can fit it in, IMHO ski resorts in the summer are great (pick one: Vail, Breckenridge,
Keystone, Copper, etc) family vacations. I've lived in Colorado my whole life and still marvel at how nice the ski resorts are in the summer. Glenwood Springs is a bit further away, but again, awesome for kids that age. Most of the mountain resort towns are loaded up with kid stuff to do.. I'd highly, highly recommend a night or two in the hills if time permits.
Have a blast!