Just off I-70 at exit #180, Vail Pass a paved trail begins that travels all the way in to Vail. The trail is called multi-recreational, open to hikers, bikers, joggers, walkers. At the start of the trail there are two lakes, these are called the Black Lakes and are open for fishing and playing.
My family visited the Black Lakes in early June. The first lake was still mostly frozen, the second had thawed. Because of the run off, there were several small creeks in the area that the kids had the most fun throwing rocks in and watching sticks flow through. The option to hike along the trail or from the dirt road next to the lakes up to the paved path above was terrific and provided us the opportunity to hike (my kids think you only go up when you are hiking) or walk and offer each individual the difficulty level they were capable of. Because the ground was soft from the runoff, there were visible animal tracks everywhere. We had a blast trying to identify who / what made each set of tracks and found it was a great learning opportunity as well.
If you driving along I-70 through the Colorado Mountains and want an easy stop for kids to enjoy nature and stretch their legs, this is a great place to stop.