Tobl, thank you very much for the very elaborate post !
It is going to take me a while to digest and think about it. And I most certainly going to watch the video.
My second question was probably indeed premature
As to the points system. The kids are pre-school. The app is about teaching them the ABC. The reason for coming up with the idea of revealing a picture is since I was not sure how much kids of this age can really grasp the idea of points ( in numbers ). I was watching some kids play games on smartphones. They do not really understand or care about points. They just want to advance and get something going on .... This is why I was thinking about revealing a picture.
Your idea of accumulating something into a shape ( like slowly charting a character, then slowly coloring it , then giving it more visible attributes ) is a good idea.
Anyway, I will think all your suggestions over and get back here for more advise Thank you very much !!!!