Durango- full day stuff would be ride that train or tour mesa verde.  Shorter duration stuff in town like raft/kayak runs down the animas, Trimble hot springs, slum around Main Street.  If you ride the train, get a seat in the enclosed cars since you can't take the kid in the bar car

Ouray- tiny but cool little town.  Hot springs in town, or the railroad museum in ridgeway.

Telluride- ski town stuff. Ride a chairlift, more slumming around town.

I'm not up on the kid friendly stuff, someone else might be.  Some of the ski hills might be running the alpine slides.

If you have a 4wd and want more windshield time the back country roads can be anything from easy dirt roads to twist a frame type stuff. Choose carefully.   A lot of those roads won't be passable till July.

If rafting is for you there are lots of places doing that.

As noted, rivers are up so rafting would be a blast.  Fishing will suck on the rivers but you may find some lakes that are fishing well.  12 YO would enjoy Glenwood adventure park, but that's about an hour or so from GJ.

Lots of mountain biking and hiking in all of those areas too.

Assuming you are coming down through Junction, stop in Ridgway to go fishing at the reservoir. Head on to Ouray and get some chocolate at Mouse's, drive up into Yankee Boy basin at a minimum (any 4x4 will make it to the bathrooms). Worst case, 4x4 tours are fun. Imogene Pass goes from Ouray to Telluride, but you definitely need a higher clearance 4x4 for that. From Ouray, head to Durango, but stop in at Silverton. Really cool old mining town! I subscribe to a extremely low carb diet, but I always stop at Durango Doughworks for a good donut. From Durango, head to Mancos then Dolores. Stop at Dolores River Brewery for a beer and good pizza. Then Telluride and hit towards Naturita/Paradox to get to Moab. There will be tons of Camping, fishing, and rafting opportunities in the loop between Ridgway and Telluride, however I can't say if the rafting will be good as I usually head up to the Arkansas River between Buena Vista and Sailda for that.

If you stop in Montrose at all, I can point you towards good food or grab a beer with you if I'm around!

ETA: The gondola is free in Telluride, so hit that!

If driving through Grand Junction take the drive over the Colorado National Monument.