The goal of this study was to evaluate immediate and delayed effects of a caregiver-implemented picture book intervention to support children's mathematical language and numeracy skills. Eighty-four 3- to 5-year-olds (M[subscript age] = 4.14) were randomly assigned to intervention (n = 40) or active control (n = 44) conditions. Participants in the intervention condition received three researcher-designed picture books with embedded mathematical language content. The active control group received similar books without mathematical language content. All families were asked to read each book a total of four times over 4 weeks (a total of 12 reading sessions). Children were pretested, posttested, and delayed (8 weeks) posttested on mathematical language and numeracy. The intervention resulted in significant positive effects on mathematical language and numeracy at the posttest. At delayed posttest, the mathematical language effects were not statistically significant, but the numeracy effects persisted. However, when only examining the quantitative language items that aligned with the intervention, the effects of the intervention were significant at both immediate and delayed posttests. Findings suggest picture book interventions can have positive impacts on children's early skills.