Empirical evidence suggests that girls work more than boys as child labor. In this paper, we develop a model to analyze the causes and consequences of the gender differentials in child labor. In particular, we analyze the effects of gender bias on child labor. We find that when parents can give strictly positive bequests to both boys and girls, son preference on its own does not lead to gender differential in child labor. Only when parents cannot give bequests, girls work more than boys as child labor. On the other hand, if there are gender differences in earnings functions, then children with superior earnings function work less than children with inferior earnings function. Our analysis shows that not only the existence of gender bias, but also its form is important for gender differentials in child labor.