Systematic biases may obscure or inflate associations with self-reported intakes. This cross-sectional survey aims to identify cognitive, behavioral, and social correlates of bias in children’s reporting of breakfast items on a self-completion questionnaire. 678 kids aged 9 to 11 years from 111 schools throughout Wales in 2005 participated. A larger percentage of less-healthful breakfast items (ie, sweet snacks and potato chips) were omitted from questionnaire self-reports. Children from lower socioeconomic status schools omitted more items than those from wealthier schools with omissions twice as high for less-healthful items than for more-healthful items within the lowest socioeconomic status schools.