Single shot bolt action rifle in 22lr. I had a Chipmunk they were very high quality and shot great. Unfortunatly Chipmunks are not made anymore.
Keystone makes the Crickett. It is ok but in my viewit is not as good as a chipmunk. You can find chipmunks on Guns America and Gun Broker still. The big plus to the Crickett is it comes in many different colors and blued or stainless. http://www.crickett.com/CrickettRifle/crickettrifle.html
remington makes a youth model 5 Savage also makes a youth model 22lr and you have heard of the Mossberg plinkster which comes as either a semiauto (Model 702)or a bolt action (Model 802).
The one thing you must remember is that the crickett and the chipmunk have NO SAFETY. Now you have to manualy pull the bolt to the rear to cock it. Some people do not like this feature but I think it is a good feature because most of the time it is too hard for a child to cock it. This makes the parent and or adult on site do nothing but moniter the child shooting.