Using multiple births as an Instrumental Variable (IV) for family size and data for 43 developing countries, I find evidence that a shock in fertility has a cost for a family as a whole. Mothers are more likely to live in less stable family arrangements and they are more likely to use contraceptives. Children are less likely to receive some vaccines, attend school, and live with their mothers. The analysis by level of development reveals the cost of fertility is driven by countries with lower levels of development.