Wow what a question. I myself find a hike anything upto an entire day and doesn't require overnight supplies and a backpack. My favorite hike which I have done a good dozen times at least is in Yosemite. Valley to top of Halfdome, 8.5 miles in, 8.5 miles out with 5000 foot elevation gain. This is about the outside of a single days event for me. My kids now 5 & 8 pull about 3-5 miles as long as the area is fun and they have food. So I am a few years off from another all day Halfdome run.