I just bought a used XSi/18-55 for my 7 year old grandson. Size and weight will be fine; he can use my 6D with a small-ish prim on it just fine. He gets the basic concepts of BBAF and shutter release. I've had him shooting manual exposure and he get the knobs/dials/meter thing in rudimentary fashion. Basics of AIM, COMPOSE, SHOOT are all there. But hey, he is 7. I can't let him take my 6D home with any lens he chooses (100-400 would just be funny!).
Which leads to my question. How many of you with kids/grandkids have them working (playing?) with SLRs at this age? Premature on my part? I started at 8, but I used a no-knobs Brownie Hawkeye. I know kids break stuff, which is why I spent big ($75 - all in) on his kit. Does any one else have the kids using 'real' camera? Just curious.