YouTube - john and me
I've got a 10-yr old that dives. He's done a number of dives including shallow night dives, spearfishing and drift dives in deeper water.
I taught him and he's not yet certified. I taught both my boys to dive, but I made then learn to freedive pretty well before using scuba gear in open water. When a small child can freedive comfortably and equalize on dives to 20 feet or so with no scuba gear, it is not hard to teach them to scuba dive.
Personally I think 10 is way too young for typical kids to learn to scuba dive, particularly in cold water were the thermal stress, extra suit and lead, large bouyancy changes and thick gloves make it much more challenging to be safe..
I make my kids wear pony bottles on pretty much all dives.