Studies using cross-sectional data have found that factors such as family socio-economic status, family structure and parental well-being have relatively weak associations with children's subjective well-being. However there is a lack of longitudinal research exploring whether early childhood circumstances, and the cumulative effect of these kinds of factors over time, exert a stronger influence. This article uses data from a longitudinal representative sample of over 13,000 children in the UK to examine the associations between family and socio-economic factors from the age of nine months to 11 years old and children's subjective well-being at the age of 11. The analysis finds that family and socio-economic factors in early and middle childhood only explain small amounts of the variation in children's subjective well-being. A parallel analysis finds that the same factors can explain much more of the variation in children's emotional and behaviour difficulties. These findings strengthen existing cross-sectional evidence on the lack of substantial socio-economic variation in children's subjective well-being and provide further the support for the distinction between correlates of positive and negative indicators of child well-being.