Children overclaim more knowledge than adults do, but for different reasons

•The construction of the first scale measuring overclaiming in children is detailed.•As children grow older, they exhibit fewer overclaiming behaviours.•Even at 10 years old, children exhibited more overclaiming behaviours then adults.•Contrary to adults, impression management may not drive overclaiming in children. Overclaiming is the phenomenon whereby people claim more knowledge of a topic than they actually have. In adults, this behavior is related to the extent to which they consider themselves an expert on that topic and may be related to impression management. We investigated the emergence of this phenomenon by developing a child-friendly overclaiming questionnaire (OCQ)—the Child-OCQ. We measured the tendency of children (5–10 years of age old; N = 94) to claim knowledge of items that did not exist for a variety of topics (places, characters, animals, food, and musical instruments). We also examined the relationship between children’s overclaiming of knowledge and their self-perceived liking of, and expertise in, the topics. To validate our scale, an adult sample (N = 51) completed both the Child-OCQ and a standardized adult OCQ, the OCQ-150, showing similar overclaiming patterns on both measures. Although overclaiming behaviors decreased throughout childhood, even children as old as 10 years were not adult-like and were more likely to overclaim knowledge than adults. In addition, we did not find strong evidence that children’s perceived expertise on a topic influenced their tendency to overclaim knowledge, suggesting that the mechanisms behind the overclaiming phenomenon are different in children and do not reflect impression management until later during adolescence or adulthood.