Before children begin school, there is a wide range of individual differences in children’s early numerical knowledge. Theoretical and empirical work from the sociocultural perspective suggests that children’s experiences in the early home environment and with informal number activities can contribute to these differences. This article draws from this work to hypothesize that differences in the home explain, in part, why the numerical knowledge of children from low-income backgrounds trails behind that of peers from middle-class backgrounds. By integrating sociocultural perspectives with a theoretical analysis of children’s mental number line, the authors created an informal learning activity to serve as an intervention to promote young children’s numerical knowledge. Our studies have shown that playing a simple number board game can promote the numerical knowledge of young children from low-income backgrounds. The authors discuss how informal learning activities can play a critical role in the development of children’s early maths skills.