That sounds lame...
OH!! I just remembered what I did in Psychology. developmental approach. We watched a video about how kids develop mentally. They showed that children under 18 months think that things only exist if they see it. If it goes out of view, it's not there anymore and they won't try to find it. They also showed like 5-7 yr olds doing things like 2 beakers of water with the same amount in, then they poured one beaker of water into a beaker that's tall and narrow. Most of them thought that the tall beaker had more water in it, because it looked like more.