PendletonCowboy:
I suggest a call to the ballisticians at Sierra. I had the exact same problem with my daughter when she was 10, with a Ruger youth model in .260 Remington and loads at the very bottom of the reloading manual.
They offered me up a recipe of 10gr. of Unique with thier 85 gr. bullet. This is actually a recipe they have for a .243, and we couldn't figure out why it wouldn't work in essentially the same case. I can't imagine them telling you any different with the 6mm.
The recoil is barely more than a .22, and my daughter became quite proficient with the rifle. At 15, she still practices with this load, but has always hunted with a full power load. I have never told her it is a different load-she may suspect it because of the different bullet, but she has never questioned me about it.
Good luck,
Sam