You could look at the MP5 or P90 airsoft guns:
http://www.tacticalair.com/aeg-airsoft-rifles-mp5.html
http://www.tacticalair.com/p90airsoftguns.html
For teaching a child gun safety I'm not sure an airsoft gun would be a good choice. I bought both my sons BB guns, a Crosman single pump for my oldest and a Red Ryder sping shooter for my youngest, when they were 10 and 7 for Christmas.
Now they are 13 and 10, are very gun safety conscious, and are into shooting my own weapons along with their BB guns. My oldest is now shooting my two pistols, my XDm 9mm and my XD 45 (5 inch tactical), and they both shoot my AR-15 A2 HBAR, SKS-D, and Ruger 10/22. The best part is my oldest has laid claim to my 10/22, so I need to buy a replacement for myself and another for my youngest.
You also need to factor in cost, both short term and long term. Most of the decent airsoft guns are going to be high double digits or low triple digits in cost (think $75 or more) and this is usually just for the gun itself, not including compressed air and/or batteries. I spent $37 for the Red Ryder, $55 for the Crosman, 2500 BB's for less than $10, and generic paper plated for 88 cents (targets). Just like the 6mm plastic BB's, I can use a BB trap and reused 100% of the .177 BB's the trap catches. With plastic BB's there are some that will break so not all of these BB's can be reused.
This also solves your problem with chambering a single round every time you want to pull the trigger. A large percentage of airsoft guns are full auto, with the obvious exception to the "sniper" rifle variants out there. With a Crosman, you have to chamber a BB every time, and then pump it.
Another drawback that I think most folks either don't realize or possibly forget about is most airsoft guns operate with batteries and/or compressed air, or some combination of both. This means you need to have compressed air, and/or charge the battery or have a charged spare onhand when you want to go shooting. With a BB gun it's grab a box of BB's and go. You can focus more on teaching the fundamentals instead of trying to find the battery/charger/compressed air can.
And if you buy a small airsoft gun, your child may end up growing out of it. The Crosman I had when I was young was passed on to my little brother and is still in use today. He's in his early 20's, and it was a hand-me-down to me from a boyfriend (at the time) of my oldest step-sister when I was about 14. I'm 36 now .... so that makes that BB gun at least 8 years older than I am.
Kris