I totally agree with you MeiLing. I have met adults that were more immature than a lot of kids. I grew up really fast and was responsible at an early age as my Son is as well. But you have to admit that as a whole, there is a difference in a 10 year old's thought process compared to, say 14 or 15 year old.
My main point being, most adults don't know how they will react in a crisis situation until they are in one much less a 10 year old. Someone may respond differently at different times to that same situation. Especially when it's their Mother or Father. It just seems, in general, to be quite a young age to me. That's all. I know my scenario is 1 in a 1,000,000, but it's plausible. I have no doubts about a kid's ability to absorb the skills and material of an OW cert. They're little sponges and are probably much easier to teach than most adults. I just have concerns regarding worse case scenarios and how responsible(me as a parent) it is to take that type of risk with them at that age. That's all.
EDIT: I've been thinking about this more and realize my thoughts were a little far out there. I was looking at it under the context of something happening to the adult that they are powerless over, like having a seizure, losing consciousness or having a heart attack. Something that the adult or skilled diver does not have control over. Looking closer at it this way, though possible, the odds are probably pretty staggering that something like this would happen.