Population-based research on children's possible prejudice against thin, obese and average body sizes is scarce. This study examined children's prejudice against various body sizes of both sexes. The effects of sex, body size, place of residence and socio-economic status (SES) on children's prejudice were also investigated. In 2005, a nationally representative sample of 10-year-old children (N = 1409) responded to a questionnaire measuring stereotypes and prejudice against thin, average-weight and obese silhouettes. As estimated by odds ratios (ORs), children were more likely to report prejudice against obesity (OR = 53, 95% confidence interval [CI]: 42-67) and thinness (OR = 20, 95% CI: 16-26) than against average body weight. The risk of being prejudiced varied with child's sex and with sex and body size of the silhouette figure. No association was found between own body weight and prejudice against various body sizes. Children with high SES were more likely to be prejudiced against obesity compared with children with low SES (OR = 1.2, 95% CI: 1.1-1.4). This large, population-based study showed that Swedish 10-year-old children hold stereotypical attitudes and are prejudiced against not only peers with obesity but also those with thin body sizes. Interestingly, no association was found between own body weight and prejudice against various body sizes.