Mothers who exceed their ideal family size (IFS) may find themselves caring for more children than desired. In the absence of reliable and desirable prenatal controls of family size, mothers may foster‐out children to reduce burdens of childrearing, particularly in contexts where fostering is common. Using six rounds of Demographic and Health Surveys collected in Uganda between 1988 and 2016, I explore the relationship between exceeding IFS and child out‐fostering, proposing that fostering‐out may serve to manage excess fertility and that this relationship may change as actual and desired fertility declines. Models are run separately for mothers and children aged 0–17 to explore mothers’ overall out‐fostering behavior versus out‐fostering strategies for children. Results at the mother level suggest a strong positive relationship between exceeding IFS and out‐fostering that remains relatively stable over time, but results at the child level indicate children's age explains the relationship between mothers’ exceeding IFS and being fostered‐out, demonstrating the nuances of how family size preferences might impact family life in practice. Though mothers report a desire for smaller families over time, childbearing and childrearing behaviors, including high fertility and child out‐fostering, remain consistent over the course of Uganda's fertility transition, signifying the central role out‐fostering plays in Ugandan families.