Miker,
My two (8 & 11 yrs old) daughter's jaws dropped when they were watching those young girls driving by with you! How old are those girls?
They demanded to know why I didn't let them drive my truck on Wentworth Spring trail!
I told them that those rigs are equipped with crawler gear set at a walking pace (Am I right?) and FJ40 is an ideal size. UZJ100 is simply out of question!!
Cheers,
I didn't really know the two younger girls. We just ran into them on the trail and happened to be at the same place at the same time. The j**ps with me were the other ones with the dudes.
My daughter is 18 and has her license, however, she's been driving the cruiser on trails since she was about 9 years old. Two years ago, she took her mom's fj40 and followed me in my fj40 down to the Dusy Ershim trail. We did about half of the trail, stayed a few days and headed back home. At 16, it was an experience she will never forgot.
As far as crawler gears, my cruiser does have them but she and my other younger daugher have driven them without crawler gears as well. My cruisr is an auto but you do need to use the gas and brake so its just not idle and steer.
As far as the Rubicon, it's a county road so an El Dorado Sheriff might be able to write a ticket if you drive without a license but but I'm not positive about that. I've never had a problem with anything like that when my daughters were younger but I don't think I've ever run across a peace officer when they were driving either.
I think you do have a bit of a point about the 40 vs. the 100. I imagine the 100 is a little harder to see out of than a 40. And as well, I'd be a little more cautious if they were driving a 100. My daughters started out driving the 40's in snow and on fire roads before they got seat time driving in the rocks. I'd recommend that you let them get some seat time on the easier stuff where they are not likely to cause any damage. Not just for your sake, but your daughters as well, you don't want them to think they hurt or crashed dad's truck the first time out. All in all, it's good experience for them and well worth the wear and tear on your nerves.

They'll remember it forever.