Concern about the effects of income and child poverty in the United States has spurred decades of research documenting the relationships between income level, family functioning, and children's development. Using data from the Survey of Income and Program Participation, this study expands on this knowledge base by considering patterns of income change among low‐ and middle‐income households with children, a population often targeted by social policies and one of growing vulnerability. A household‐centered growth curve analysis first identified statistically significant variation in intrayear household income level over the period of the study. Cluster analysis was then used to distinguish between groups of households according to their distinct patterns of income instability using measures of frequency, magnitude, direction of income change, and income level. This work begins to establish a descriptive empirical evidence base of the realities of household income dynamics that has implications for future research, policy, and practice.