Police report it as an accident, but didn't release any further information.
Apparently pellet guns aren't harmless.
Update (1/26/12): From an article:
“BB guns can kill a person. High-velocity BB guns, which have muzzle velocities higher than 350 feet per second, can increase this risk,” according to the U.S. Consumer Product Safety Commission.
About four deaths a year are caused by BB guns or pellet rifles, according to the CPSC.
“Many people do not realize that BB guns, especially high-velocity guns, can cause death. Therefore the CPSC warns that children under 16 years of age should not use high-velocity BB or pellet guns. And, like firearms, these guns should never be aimed at another person.”
Clearly this sort of dangerous behavior had gone on for some time, as evidenced by the evidence of extensive shooting and number of pellet guns this boy had:
Officers found numerous Airsoft guns upstairs in the boys’ bedroom and the bonus room, according to the report. Two Airsoft rifles and two pistols were located in the boy's bedroom. One rifle was leaning against the wall next to the closet. A rifle and a pistol were located on the bed and the other pistol was on a chest of drawers.
A zip lock baggie containing numerous CO2 cartridges used in pellet and Airsoft guns as well as a baggie containing pellets were located on the dresser, Cpl. Todd said.
There were numerous Airsoft rounds on the ground throughout the upstairs.
In the bonus room where the shooting took place, there was a small child's chair approximately four feet from the window. An open metal container of pellets was located on the ground near the window and a clear plastic container of BBs was on a small table near the chair.
Also, there were the hand-drawn targets in both rooms that had damage consistent with being shot with a BB or Airsoft gun.
The trees located across the driveway from the window had damage consistent with being struck with BBs and pellets, the report said. The driveway and yard were littered with Airsoft pellets.
Every gun in the hands of a child must first pass through the hands of an adult.