My dad uses IMR SR4759 in his 308's. He teaches Hunter Ed classes at his range and thats what all the kids shoot. Its a pistol powder but works excellent as a reduced load powder in the 308 because it is so bulky and takes up the extra space.
I believe you can find reload data for it in the speer manual and a few others. If you decide you want to give it a try I can provide you with some data, I know I have it in a few of my books.
Probably the lightest load you will find for a kid, no good for hunting though.
Dave