My kids are DD12, DD10, DS7 and DD3. When the oldest was 10, I would leave the next 2 with her for short errands (no more than 30 minutes), but the youngest would come with me. When she was 11, I started leaving the youngest with her too, but only for periods no longer than 1 hr and only when the youngest agreed (as in no crying). Now I will leave the oldest in charge for longer periods, but not for any real length of time at night. (meaning DH and I still can't go to a movie or dinner without an older sitter; read: grandma).
I also will let the 10 yr old watch the 7 yr old for an 1 to 1.5 hrs and I let her watch the 3 yr old for short periods of time (ex. I have to leave to take the oldest to an activity and DH is on his way home). But I will say my 10 yr old is very responsible. If my DS was the 10 yr old, I wouldn't do it. He just wouldn't watch the 3 yr old. Also the 3 yr old has always done very well with her older sisters. She seems to think she has a mom and 2 sort of moms.
I think it depends on the kids. With your kids ages, as long as you are sure they will behave, I'd absolutely let the oldest watch them. But here are my rules:
1. no answering the phone unless caller id shows it's me or their dad. NO ONE ELSE, even grandma!!
2. no phone calls to friends, only calls to me or their dad.
3. NO cooking. NO microwave or toaster oven. NONE ever.
4. no answering the door.
5. no going outside, even to the backyard.
6. no showers or baths.
7. at least attempt to get homework done
My kids usually enjoy the responsibility. I also pay the older 2 when they babysit the youngest (not the 7 yr old.). I don't pay much. Actually I've never given them any cash. They keep a running account and I will pay up when they are owed enough to warrant paying and when they have an acceptable (to me) item they wish to buy. This means no spending on candy.
