How did you decide on age groups?

We haven't officially decided yet, but we talked a lot about this last night, and we decided to keep the oldest age we would take at a year younger than our youngest child. So that keeps us with a pretty young age range, but I think we are planning to take boys or girls, so hopefully we won't end up with zero placements. I worry that with such a young age range that there will be a lot of other foster homes that want the same.