Improving children's lives is high on the UK policy agenda. In this study for a recent birth cohort of UK children we examine how three aspects of parental resources – income, mother's mental well-being and family status – in early childhood enhance or compromise their children's cognitive and behavioural development. As well as examining how these three aspects of parental resources separately and jointly affect children's well-being, we also enquire whether persistent poverty or persistent maternal depression are more deleterious for children's current well-being than periodic episodes of poverty and depression. We find strong associations between poverty and young children's intellectual and behavioural development, and persistent poverty was found to be particularly important in relation to children's cognitive development. Maternal depression (net of other factors) was more weakly related to cognitive development but strongly related to whether children were exhibiting behaviour problems, and persistent depression amplified the situation. Family status, net of other factors (most noticeably poverty), was only weakly associated with children's development.