Despite dramatically narrowing gender gaps, women remain underrepresented in mathematics and math-related fields. Parents can shape expectations and interests, which may predict later differences in achievement and occupational choices. This study examines children's early mathematical environments by observing the amount that mothers talk to their sons and daughters (mean age 22 months) about cardinal number, a basic precursor to mathematics. In analyses of naturalistic mother-child interactions from the Child Language Data Exchange System (CHILDES) database, boys received significantly more number-specific language input than girls. Greater amounts of early number-related talk may promote familiarity and liking for mathematical concepts, which may influence later preferences and career choices. Additionally, the stereotype of male dominance in math may be so pervasive that culturally prescribed gender roles may be unintentionally reinforced to very young children. © 2011 SAGE Publications.