No I wouldn't. Completing a course and knowing how to perform first aid doesn't give you knowledge about how react emotionally with a crying baby. That only comes with maturity and experience (yes I know you can't get experience if no one lets you do it, but get used to that, it happens in the job world too!) I can't see a 12 year old with a crying baby that won't stop for an hour not getting stressed and freaked out. I'm saying this because I was a 12 year old babysitting, and I didn't have a clue what I was doing. The baby was asleep when I got there and stayed asleep, but if it had woke up, I would have been screwed. I personally wouldn't hire one under age 15. But that's just me. One idea, since you do need to get experience somehow, one person had a good suggestion.. a mother's helper. I would have no problem letting a 12 year old help me with the baby if I was there. I would show her how to take care of the baby and how to react when the baby is upset, and let her do the work so she learns the ropes. Call it on the job training.