I was 11 when I started to babysit for money (for kids in our neighbourhood) and had a pretty good business going by the time I was 12/13! I was a very mature (looking and acting) and responsible kid, but I'm not sure I'd trust someone that young with my kids now that we're in the planning stages of our own family! Who knows. It would depend on the kid!
I was even younger when I started watching my brothers, (one six years younger and one 11 years younger), unpaid of course.
My Mom and Dad got lots of childcare out of me, now that I think of it! Some of my favourite childhood memories are from these times, though- I used to sing to my brothers at bedtime- taking requests!
Firm favourites were "Wildfire" and "Maybe" from Annie hehe Such nice memories!
Aww...only I can get weepy over a babysitting thread!