Child subjective well-being is determined by various personal, social, and contextual factors. Few studies have found reliable differences in the prediction power of these factors; however, the results vary especially when it comes to sociodemographic factors, such as the effect of child’s socioeconomic background on life satisfaction. This paper examines how poverty and social relationships affect the perceived life satisfaction of Finnish schoolchildren. Drawing on survey data of Finnish schoolchildren, from grades 5, 7, and 9 (n = 1793), linear regression was used to test how life satisfaction would be associated with socio-demographic variables, poverty, and child–parent and peer relationships. The results emphasize the complex nature of the determinants of children’s life satisfaction. The greatest unique contribution for change of life satisfaction was made by the time spent with mother (β(p) = 0.189). Overall, the model showed a good fit (R² 19.9). These findings have important implications for family policies and services that promote good parenting and positive parent–child relationships. Furthermore, this study highlights relational well-being as a key determinant of children’s life satisfaction.