We examine the long-run effects of the pay-as-you-go (PAYG) social security scheme on fertility and welfare of individuals in an overlapping generations model, assuming that child-care services are available in the market. We show that the impact of a tax increase on fertility depends on the relative magnitudes of the standard intergenerational redistribution effect through the social security system, the (implicit) subsidy effect through tax-exemption of child rearing at home, and the price effect through changes in the relative price of market child care, and that if parental child-rearing time is inelastic, a tax cut could bring about a Pareto-improving allocation.