We use the matched mother-child data from the 2000 wave of the US National Longitudinal Survey of Youth 79 (NLSY79) to assess the impact of full-time working mothers on children’s body mass index (BMI) and the likelihood of becoming overweight. Parametric, semi-parametric and non-parametric methods are employed to correct the bias of selection on observables and unobservables. Pros and cons of various methods are discussed and specification tests are conducted. In general, we find that a mother’s full-time employment does have some impact on her children’s BMI and likelihood of becoming overweight across models and inference procedures.This paper was publised in Journal of Econometrics 152 (2009) 61-69