The child Supplemental Security Income (SSI) caseload increased by nearly 40 percent between 2002 and 2012, from just over 900,000 to nearly 1,300,000, and the upward trend shows no signs of reversing. In this descriptive paper, we explore the nature of the caseload growth over this period. Consistent with previous studies, we find that national trends in child SSI participation are driven by growth in cases diagnosed with mental impairments, which more than doubled over this period. Our state-level analysis reveals that the national trends mask significant variation across states.