Maternal self-efficacy (MSE) has been shown to be important, yet little is known about how it develops over time and whether increasing knowledge about child development and parenting results in feeling more efficacious, especially for first-time mothers. Furthermore, research is lacking about whether increased maternal self-efficacy results in better child outcomes such as more receptive and expressive language. Using a randomized three-group design, this study explores whether educational books, embedded with information about typical child development and optimal parenting, increase MSE for women over the first year and a half of motherhood and whether these increases result in better language skills for children at 18?months of age. Hierarchical linear model analyses show that MSE starts high and remains high and that providing educational books further increases the development of MSE. Increases in MSE have a positive impact on children's language skills, as does providing books, irrespective of educational content. These findings support the importance of MSE and demonstrate an inexpensive way to increase MSE and improve child outcomes.