As far as I know, NHTSA and IIHS don't conduct any rear ender vehicle crash tests. Nonetheless, I would personally insist on having my child riding in the Wrangler's rear seat properly restrained in an appropriate carseat. This is because frontal collisions are statistically the most common type of crash, while rear end collisions are among the least frequent type of crash. Severe rear end collisions tend to be rarer still since the vehicles involved are usually traveling in the same direction and/or may be already slowing down prior to actually colliding. Someone else on the board here can probably post a handy graphic illustrating the statistical frequency of crash types comparing frontal/side/rear, etc. Basically, the farther you or your passengers are from the windshield and engine block, etc. in a frontal crash, the less likely you are to be injured or worse if you are properly restrained.
Other Jeep owners who frequent this board have been able to install carseats in the back seat. It can be done. If you search for past posts using "Jeep" or "Wrangler" as your search criteria, you can probably find some of the threads discussing seats installed in Jeeps.
Given the greater likelihood of a frontal crash vs. a rear end crash, I probably would argue for restraining a child in the back seat even if the vehicle were an old recalled 1970s model Ford Pinto, notorious for bursting into flames when rear ended due to a gas tank design flaw.
Then again, I'd rather walk than drive a Pinto.
But seriously, if the Wrangler has a back seat and a compatible child carseat can be properly installed there, the back seat would be the place for a child to ride.