Parents’ judgments about their children’s level of interest in different science topics may affect the science-learning opportunities they provide their children. However, little is known about how parents judge these interests. We used the truth and bias model of judgment of West and Kenny (Psychological Review [2011], Vol. 118, pp. 357–378) to examine factors that may affect parents’ judgments of their children’s science interests such as the truth (children’s self-reported interest) and potential sources of parental bias. We also investigated whether several individual difference measures moderated the effect of truth or bias on judgments. Children (N = 139, ages 7–11 years) rated their level of interest in five science and five non-science topics. Separately, parents (N = 139) judged their children’s interest in the same topics. Overall, parents accurately judged their children’s science interests, but we also found evidence of some forms of bias, namely that parents generally under-estimated their children’s science interests. In addition, parents’ personal science attitudes were related to judgments of science interests, such that parents more favorable of science tended to rate their children’s interest in science topics higher than parents with a less favorable view. We did not find evidence that individual differences among parents moderated the effect of truth or bias on judgments; however, parents were more accurate at judging the non-science interests of older children than younger children. Parents should be aware that they may be under-estimating their children’s interest in science topics and that their personal attitudes about science may be influencing their judgments of their children’s science interests.