Go for it- I would bet that an equal amount of us started for caring for sibs when we were about that age, without the benefits of red cross baby sitting courses, cell phones, 911 or share rides and cabs.

I was nine when my mother went back to school one afternoon a week and I started caring for my baby twin sisters. By the time I was 11 I babysat them three afternoons and two evenings a week in addition to cooking dinner for my father. It will give them a chance to grow, and discover a bit of preplanned independence.