This dissertation estimates the average treatment effects of a mother's full-time employment on children's body mass index (BMI) and likelihood of becoming overweight. The matched mother-child data from the 2000 wave of the U.S. National Longitudinal Survey of Youth 79 (NLSY79) are used. In the first part of the dissertation, the econometric methods correcting the bias from "selection on observables" including control function and matching based on propensity score, are applied to perform the estimation. In the second part, the econometric methods correcting the bias from "selection on unobservables" including maximum likelihood and semiparametric approaches, are used to conduct the estimation. It is concluded that, on average, the group of children with full-time working mothers have significantly higher BMI and a greater likelihood of becoming overweight.