The AR platform is a soft shooting gun.

A .223 with a well constructed bullet will do the job, if placed right behind the ear.


Some of these young kids "can" shoot.


I like this for a truck gun and will work for kids also.

http://www.ruger.com/products/mini14...le/models.html


My biggest concern is that they are both autoloaders - although maybe just limit the amount of rounds in the magazine to start (safety precaution).