Early August water will be low most places
We have 2 young kids and did Labyrinth in June. Lots of rowing with the headwind.
I don't know where you are driving from but from front range it is still 6 hours to Green River put-in.
The Upper C could be multi day (Pumphouse to Burns) but the railroad at night was a killer for us.
Yampa was a nice float (South Beach to Duffy Mt) last week but it was getting pretty low.
Gunnison River (Dominguez Canyon) is another nice one.
If you can score a permit on the San Juan that is what I would do. We loved that. We floated from Bluff to Mexican Hat.