JDoyle,
I also coach a group of kids and you are right. We have the most fun shooting at the dollar bills. What I do is fold the bill so that the middle portion of the bill is the only thing you see. (George' s Head) then we play if you hit it then you get it. The catch is you must hit george. (THIS IS IN NO WAY INTENDED TO DISRESPECT GEORGE WASHINGTON, I even discuss this with the kids). I have also expieremented with larger bills but that can get expensive. The larger the dollar amount the more focused the kids get.