From fs.usda.gov-Drive 9 miles north of Flagstaff on US 180 and turn west (left) on FR 245 (at milepost 230). Continue 3 miles to FR171 and turn south 1 mile to where FR 171B turns left a short distance to Lava River Cave.
We took our 4 kids on this hike ages 1,3,6,8 and had a blast! I would not recommend carrying kids on this one. I had a baby in a sling and it was really hard, my legs felt like jello for a couple days!. It is a pretty busy trail, with a constant stream of people in and out. It is dark inside, and can get chilly, so a headlamp is a must and a sweater or light jacket. Most of it is crawling over rocks and boulders, so you will need your hands free. Our kids did ok, some were scared of the dark, I turned around before the end with the younger kids. This is one where they need to take care of bathroom needs before they go in, and carry your trash out too. It was a fun experience and I can't wait to try it again with my older kids. I think a good age group would be 4 and up.