child psychology experiment

http://www.youtube.com/watch?v=y9DxgM0vpsA&feature=related

This is a video about a child psychology test.  An adult had two of the same sized cups of water and one empty tall glass. The child understood that the water was the same amount when they were in the small glasses, but then once the lady poured the water into the tall glass he immedietly thought that the tall glass now had more water. The little boy could not understand that the amount of water did not change.