Recent literature has shown consistent evidence of a positive relationship between maternal employment and children’s excess body weight. These studies have mainly focused on the effect of average weekly work hours over the child’s life on its overweight or obesity status. This paper attempts to explore whether the timing of maternal employment with respect to the child’s age is an important factor in this relationship. Data on a nationally representative British birth cohort are used to examine this; the 1958 National Child Development Study. The results show a significant positive correlation between maternal employment at age 7 of the child and the probability that a child is overweight at age 16. Additionally, the analysis shows it is full-time as opposed to part-time employment that increases the child’s weight. Subgroup analysis suggests this effect is driven by the lower socio-economic groups. Various econometric techniques are used to explore possible unobserved heterogeneity, but there is no evidence that the estimates are biased.