Why I Chose Horn Fork Basin ?
Our goal for Day 3-4 was originally to hike up Mt. Columbia, a 14'er in the Collegiate Peaks range.  There are several trails to choose from, but I had hiked Mt. Harvard (2002) and enjoyed the North Cottonwood TrailHead (TH) route.  It's about 5.5 miles back to Harvard for a roundtrip of 10-11 miles.  Mt. Columbia is along the trail at about the mid-point.
I had chosen this trail for several reasons.  First and foremost, the trail was kid friendly in many ways.  Starting at 9,800ft the trail was very gradual in its increase in altitude.  Second, the first 3 miles of the trail goes through fairly thick forests and has several streams to cross, some by bridge some by foot. Additionally, the trail varies from even dirt path, to rocky parts, to sections alongside mountain sides with gentle rolling dropaways (minimal danger), to two snow avalanche areas, to semi-marshy areas once you reach the basin.  All of that diversity makes it interesting for kids to hike through.
This trail also offers flexibility in objectives and good camping sites.  Though he had trained well, I wouldn't know ahead of time how Cole would do on the hiking a 14'er, so if we determined that it was 'not doable', then there was also Bear Lake as an option to hike up to. 

The are also numerous good camping sites within the forested trail, with a good camping area at between the 2.5-3 mile section of the trail (about 1/4 mile before treeline), with the stream running alongside  about 100 yards off to the southwest of the trail.  For those that don't mind a more open campsite, there are also good sites just beyond the edge of the treeline, with some brush and small trees for additional wind shelter.