If you have time to hike into the canyon on only one trail, the Bright Angel Trail, though popular and steep, is a good pick. When my son was seven, we hiked 1.5 miles in the July heat down to the first rest house and then headed back up. The path rewards hikers with sightings early on of fossils of branchiopods (ancient shelled creatures), corals, sharks and sponges in the canyon walls. The further down you go, the more the crowds thin out. With older kids, continue on, but on a summer day heed the rangers’ advice to turn around at Indian Garden, 4.6 miles. Remember to tote lots of water.