In the light of recent research concerned with children's understanding of mind, a study was conducted in order to test the hypotheses (a) that only older children (i.e., 8-year-olds) would understand that emotional states can influence cognitive performance, but (b) that both older and younger children (i.e., 5- and 8-year-olds) would understand its influence upon cognitive motivation. Children were explicitly questioned about the consequences for cognition and motivation of negative affect. Results based on children's predictions and justifications provided substantial support for the hypotheses.