Taking family structure, father's work intensity, and children's developmental stages into consideration, this study examined the effect of a mother's previous and contemporaneous work (employment and weekly work hours) on their children's weight and their likelihood of having weight problems such as obesity, overweight, and underweight. Using data from the Early Childhood Longitudinal Study-Kindergarten Class of 1998-1999 (ECLS-K), this study adopted a fixed effect model and found that for 3rd to 5th graders, an increase in mothers' previous work hours among two-parent families below the federal poverty level (FPL) increased the risk of the child being obese, while the current employment of single mothers below the FPL reduced the risk of the child being obese. Surprisingly, the employment of single mothers below the FPL increased the risk of the child being underweight, especially for 1st to 3rd graders.