IMHO, at this age the emphasis should be on proper mechanics, using the legs to supply the power and not the arms, instead of emphasizing velocity or even throwing strikes. Both velocity and strikes will come when the child is comfortable and throws properly without thinking about the mechanics. A child can get away with throwing hard in LL using only arms, but as they move up to bigger fields and better hitters, they’ll be blown away.
Personally, I’d rather loose some game time at age 11 to teach correct mechanics than to loose game time at age 13 because my child relied upon size and strength instead of proper throwing mechanics when he was 11. As for drills, I think simply practicing and not allowing the child to get away with throwing only with his arms works. I have a few nice bruises from watching my sons’ mechanics instead of the ball when catching. This is the 1st year my 12 yo (5’-9") has pitched, and mostly because we’ve been working on his mechanics the last several years, and because he’s been horrible. It’s pretty impressive to watch a kid who is not even considered athletic to come from “nowhere” and to have command of four pitches. The kids who have been pitching since they were 8 and relied on their athleticism are slowly taking a back seat 'cause they never learned the art of pitching.