Scholars have argued that becoming a parent affects political behavior, including turnout. In this article, we identify the effect on turnout of having an additional child conditional on the decision to become a parent. When parents have a child, nature sometimes assigns additional children through twinning. We argue that conditional on age of parents and birth cohort this as-if randomly assigns an extra child to some parents. With a large data set of family composition and validated turnout for Danish voters, we find, consistent with additional children taking up parents’ time and indirectly increasing the cost of voting, that having an additional child 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 to vote across three elections. For fathers, turnout is only depressed by 0.7 to 1.4 percentage points.