Introduction: Decision-making on the desired quantity of children is one of the most important episodes of family life cycle that has far-reaching outcomes. One of these outcomes is quality (human capital) of children. If there is a relation between quantity and quality of children, determining quantity of off-springs could not be independent from quality. This paper investigates the relation between the quantity and health of children.

Method: Deductive reasoning is the analytical method in this study. Therefore, it is theoretically discussed the relation between quantity and quality at first and then hypothesis is empirically tested. For this, the data from 10 years old students in Tehran is used to estimate regression equations.

Findings: The sample includes 1294 observations. The results show as the quantity of children increase in family, the height and weight of them would decrease. This evidence confirms that the large family cannot be a suitable environment for rearing children.

Discussion: Regarding to the trade-off between quantity and health of children, it seems that the increase of family size and fertility growth would damage the physical ability of individuals and future labor force.