This study examined whether children's formal and informal home literacy (HLE) and home numeracy (HNE) environments at 3 years old demonstrated domain-specific, and cross-domain effects on children's academic performance at 5 and 9 years old. Participants were 7,110 children (49.4% male; 84.4% Irish), recruited between 2007 and 2008 in Ireland. Structural equation modeling revealed that only the informal HLE and HNE demonstrated both domain-specific and cross-domain positive effects on children's language and numeracy outcomes but not on socioemotional outcomes, at 5 and 9 years old. Effect sizes ranged from small ([beta] = 0.020) to moderate ([beta] = 0.209). These results suggest that even casual cognitively stimulating activities that do not directly focus on active teaching may benefit children's educational outcomes. Findings bear implications for cost-effective interventions with far-reaching, and enduring, effects across multiple child outcomes.