The best general advice I've discovered is in Lisa Gollin Evans's book An Outdoor Family Guide to Yellowstone and Grand Teton National Parks (Mountaineers Books, 2006). Older children can learn about nature by enrolling in the Yellowstone Junior Ranger Program. The Young Naturalist program at Grand Teton provides children with a similar opportunity to explore the natural world of the park and costs $1.
The Young Naturalist program at Grand Teton provides children with a similar opportunity to explore the natural world of the park, following instructions from an activity brochure. It costs $1 to participate; when you complete the course, you're awarded a patch.
Children (ages 8-14) visiting the park are encouraged to explore and experience Grand Teton as members of the Junior Ranger program. To participate, pick up a copy of the Junior Ranger activity brochure at any visitor center, and then complete the projects outlined in the booklet during your stay. When you present a completed project (and $1) to a ranger at the Moose, Jenny Lake, or Colter Bay visitor centers, you'll be awarded a Young Naturalist patch.
Two trails within Grand Teton are especially kid-friendly. At 7 miles round-trip, the entire Jenny Lake Loop Trail is a bit long for kids, but take the boat shuttle across Jenny Lake to the Inspiration Point Trail portion, which is less than a mile long. The Christian Pond Trail, a level, 1-mile round-trip from the corrals at Jackson Lake Lodge, is also a nice diversion, offering great views and a chance to see myriad waterfowl.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.