In this quantitative study, we investigated the relationships between parenting and young learners' English learning--specifically parents' sociocultural influence on elementary school children's motivation--within the framework of self-determination theory (SDT). We surveyed 212 dyads of Japanese parents and their children (8-12 years old) and used structural equation modeling to elucidate the causal relationship between parents' attitudes and children's motivation for their second language (L2) learning, which is English as a foreign language learning context in this study. We found that parental involvement in children's English education positively impacted children's perceived competence in L2 learning and their interest in other countries, improving their L2 learning motivation. This demonstrates that parental involvement is a significant predictor of young learners' L2 motivation in Japan. We also identified a discrepancy between children's and parents' perceptions. Parents believe their involvement in children's L2 learning is autonomy-supportive behavior, while children do not always perceive this. We conclude that parental involvement in children's home L2 learning supports children's learning motivation. Our final model expands the SDT framework for language learning and covers both parenting and language learning research realms, improving our understanding of how parental attitudes and behavior influence children's L2 learning.