Our understanding of trends in family complexity from the perspective of children is limited, despite potential implications for child well-being. This paper extends recent prevalence estimates of children’s exposure to sibship complexity, relying on the unique genealogical design of the Panel Study of Income Dynamics (PSID, 1985-2017) to follow successive cohorts of children and identify sibling relationships within and beyond households. Our preliminary descriptive analyses map the share of children with full, half, and step siblings over the first 15 years of life. We find increases in the overall prevalence of sibship complexity across cohorts of children born in the late 1980s to the early 2000s. Prior to PAA, we will further explore variation and change by mothers’ union status at birth, race and ethnicity, and education. This work will set the stage for a more detailed analysis of family complexity and links to child investments within and across households.