Susan Dalton has a wonderful column this month on a class of real little ones
http://www.aikiweb.com/forums/showthread.php?t=22878
I think it's wonderful, but I'm not really into kids that much and was happiest some years ago assisting with a class of 7 to 11 year olds - they can focus and learn. Ikkyo, iriminage, kotegaishe, etc all are fine as long as they aren't cranking...and since adults shouldn't be cranking for pain compliance, makes sense to me to start teaching it from an early age!