Acting in an unpredictable manner on the one hand and trying to guess out another person's behavior on the other hand can be a quite valuable ability. Research show that professionals and chimpanzees have this ability. We conduct a field experiment with kindergarten kids to test the ability of playing minimax and compare the behavior of kids with university students. We find that children's behavior shows more serial correlation than adults and they more often switch their strategies independent of the success rate. The variance is relatively high among adults but interestingly small among kids. Our results rather suggest that even though humans usually never get very good at behaving in an unpredictable way they certainly get better in that from childhood to adulthood.