Research on the development of metamemory has focused primarily on children's understanding of the variables that influence how likely a person is to remember something. But metamemory also involves an understanding of why people occasionally misremember things. In this study, 5- and 6-year-olds (N = 38) were asked to decide whether another child's mistakes in a memory game were due to false memories or guesses. Some of the fictitious child's mistakes were similar to material he had seen earlier and some were not. Six-year-olds, but not 5-year-olds, consistently attributed more similar than dissimilar mistakes to false memories. Understanding the link between similarity and false memories improves significantly between 5 and 6 years of age.