I highly recommend Red Rocks, it has some of the most beautiful views and great hiking/biking trails. You can get to it by getting off C470 at Morrison Rd. You will then go through the town of Morrison (One of the coolest towns, I highly recommend walking through it and seeing the stores) and then take the Red Rocks Entrance (Entrance 3 is better, in my opinion).
Hi for family friendly hikes there's also Grand County. It's chalked full of hiking for any taste. There's also indian peaks wilderness between the front range and grand county where you can find any number of trails for the fam as well.
White water rafting is also an experience worth considering while you're in Colorado. You have different levels, ranging in classes 1-5, so it can be a family-fun activity as well as a fun, exhilarating one.
I highly recommend Red Rocks, it has some of the most beautiful views and great hiking/biking trails. You can get to it by getting off C470 at Morrison Rd. You will then go through the town of Morrison (One of the coolest towns, I highly recommend walking through it and seeing the stores) and then take the Red Rocks Entrance (Entrance 3 is better, in my opinion).
+1 on what he said. Red Rocks is very nice and it is a very close drive to everything in the denver metro area.