What are the foundational abilities that young children must develop at the beginning of school for their future academic success? Little is known about how emotion knowledge, social behaviour, and locomotor activity are associated and how these abilities may be predictors of academic-mathematic performance (less correlated with the children’s SES than pre-reading and linguistic achievement) in a large cohort of preschool children. Here we show that emotion knowledge, locomotor activity, social behaviour, and academic-mathematic performance are interrelated in 706 French preschool children aged 3 to 6. Mediation analyses reveal that the increase in academic-mathematic performance is explained by the increases in emotion knowledge and social behaviour and, in turn, children with a greater comprehension of emotions tend to have better locomotor skills and higher academic-mathematic scores. Additionally, sequential mediation analysis reveals that the increase in emotion knowledge, locomotor activity and social behaviour partially explains the increase in academic-mathematic performance. These results are discussed in relation to three possible mechanisms. Our findings are consistent with the political and scientific consensus on the importance of social-emotional abilities in the academic world at the beginning of school and suggest adding locomotor activity to these foundational abilities.