there are tons of drills out there that you can find helpful. I want to tell you to work on speed, conditioning and base running during practice. I highly recommend finding a strength coach in your area and see if he/she will come out to a practice and work with your team on running technique. Boys, aged 11-12 are in a great "developmental zone" where you can teach them technique. Base running is a highly overlooked aspect to the game. I would finish practice with some base running games or other "conditioning" activities disguised as games!
You can only work on hitting for so long, don't forget about the "overlooked" aspects to the game.
Hope this was helpfull. Please feel free to contact me personally at firstname.lastname@example.org or check out my Ebook at www.conditionedtohit.com