Wow. I know this usually varies by region but I'm feeling really cheap!
Our summer sitters are teenage girls (they rotate days and aren't working every week) and we are paying them $8 per hour for an 11 year old and an 8 year old, and they are here 3-4 hours a day. I usually round up and kick in a little extra because gas is so high plus I make sure there are things here for them to eat for breakfast and/or lunch depending on when they are here. I asked around and found people paying $6-$10 an hour so I split the difference.
See I actually think that is a pretty good rate. Most of the ones that were talking higher were younger children. With an 8 and a 10 year old they mostly would entertain themselves you have no messes to really clean up, no diapers, they can get themselves a drink so you don't have to... mostly making them lunch and just making sure no one burns the house down.
When I babysat I was watching a 7 and a 3 year old. The 3 year old was the work, the 7 year old I might read a story with or play a game while her brother was doing other things but she really didn't take much work.