Thanks for the lesson, it looks like a good one. I think I'll try this with my kids soon. If I can find the right pictures, I might expand it to non-verbal gestures in general as well.
One thing, I'm an Aussie, and I've never heard of those interpretations for either hand singns you mention us in. Thumb and index finger making a circle has always meant OK to me, and using the index finger to call people to you hasn't got anything to do with prostitutes. We'd be more likely to use it with little kids than adults though.