Scholars have argued that becoming a parent impacts political behavior, includ-ing turnout. In this paper, we identify the effect on turnout of having an additionalchild conditional on the decision to become a parent. When parents have a child,nature sometimes assigns additional children through twinning. We argue thatconditional on age of parents and birth cohort this as-if randomly assigns an extrachild to some parents. With a large dataset of family composition and validatedturnout for Danish voters, we find, consistent with additional children taking upparents’ time and indirectly increasing the cost of voting, that having an additionalchild at the same time as another depresses turnout for both parents. Mothers’who had twins in their first parity are 1.6 to 3.0 percentage points less likely tovote across three elections. For fathers, turnout is only depressed by 0.7 to 1.4percentage points.