You may want to look into getting a new stock instead of cutting one down, unless you're into woodworking.
Blackhawk Axiom... Collapsible 6 position that will grow with your child. It will also take almost a pound off the rifle. Don't forget to get the cheek piece. It also free floats the barrel.
"With great power, there must also come great responsibility." - Stan Lee
"All that is necessary for evil to triumph is for good men to do nothing." - Edmund Burke