Family change has important implications for child and adult well-being across all development stages. At the global level, however, the changing structure of families is inadequately documented. This paper fills this gap, focusing on family change at young and primary adult ages. Our analyses draw on 30 years of survey data from three million respondents across 84 low- and middle-income countries (LMICs). They document global and regional-level associations between Human Development Index (HDI) and novel indicators reflecting multiple dimensions of family change. Significant declines in fertility, delays in the transition to adulthood, and shifts towards more gender-egalitarian attitudes within households have occurred with development. Yet, our analyses also show that families in LMICs have changed in ways that are at odds with existing theories of family change: the average number of years adults spent in unions has stayed relatively constant, and intergenerational coresidence has declined only weakly with development. Regional trajectories of family change remain distinct, indicating rather slow, if ever, global convergence to a Western notion of the nuclear family. Alongside the persistence of key dimensions of family life throughout the development process, our findings suggest a continued centrality of the family despite profound social and economic changes in LMICs that have affected sexual practices, marriage, fertility, gender norms, and economic activities within and outside the family.