My mom took my little brother to participate in a child psych study like this when he was a toddler (mom had some ties to the university). It was a very similar experiment with skittles as the prize. My brother sat staring glumly at the candy the whole time. The test administrator was increasingly enthusastic with praise after each round right up until the end when she congratulated him and said that he could have the whole bag. He said "no thanks" and ran back to mom crying because he was told there would be candy but they only had skittles, which he very much did not like (and for that matter still doesn't). The administrator was apparently embarrassed and told my mom that she thought that all kids liked skittles....