T.W.
I start my kids at age 10 for short periods--now and then (not every day, I would not agree with that), then at 12 for longer times. My kids are both VERY trust worthy!! Now my DD is almost 14 and she is baby sitting other kids. I was baby sitting at 11.
You have to know you kids......each child is different. There are Home Alone classes through Parks and Rec. if you would like them to be prepared for an emergency......I highly recommend them!!