Good Post, .. and brings back some memories.
The AR is one of the favorites of my boys. I am now learning to call this the MSR (or Modern Sporting Rifle *)
As they were growing, I would work with one of them on the firing line, while the other was struggling to load 'his' magazine.
The MSR, provided safe shooting; my young sons could keep the barrel pointed down-range on the target and enjoy multiple shots without having to manipulate a bolt or lever. 30 rounds allowed them an opportunity to understand the shots and 'try better' next time.
Bolt-Open devices help to ensure that the gun is empty and increases safety. After a quick double check, I would let them eject the magazine and show me the gun was safe.
Then my next son, would start his fun.
* MSR thread at http://www.firearmstalk.com/forums/f20/moving-away-ar-msr-76567/index3.html#post1019035
has my put on the MSR.