Imagine yourself seated next to your 10, 11, or even 12 year old while you watch 12-18 year olds beating each other to death, stabbing each other with blood spurting, and shooting each other at point blank range (does it really matter that it's arrows and not guns?). Close your eyes and really imagine. If any of this makes you uncomfortable, then you know deep down the answer to whether or not a preteen should see this movie. Yes, there is a good overall message, but it will be missed by even the brightest child because their young minds will be trying to cope with seeing such violence. Consider this: until adolescence, your child's brain is going through a process of "synaptic pruning." This pruning starts near the time of birth and is completed by the end of puberty. Pruning is influenced by environmental factors and is widely thought to represent learning. This neural immaturity is what accounts for the relative ease with which children learn. Input they receive makes a psychic imprint on their minds. Now ask yourself, "Do I want to imprint my child's mind with violence?"
Ironically enough, this happens to be the "good message" of the film - doing what's right even though others pressure you not to. So do what's right and tell your kids, "not never, just not now."