Majority of US children enroll in Medicaid, many face coverage gaps by age 18

Embargoed for release: Wednesday, September 24, 2025, 11:00 AM ET

Key points:

• By their 18th birthday, 61% of U.S. children have relied on Medicaid or the Children’s Health Insurance Program (CHIP), and 42% have experienced gaps in coverage, according to estimates from a microsimulation model.
• Disruptions to insurance coverage were more common among children covered by Medicaid or CHIP at birth in states that did not expand their Medicaid adult programs. States that set the most restrictive income eligibility thresholds for children under Medicaid and CHIP saw the highest share of coverage disruptions.
• The findings highlight the broad reach of Medicaid and CHIP, suggesting that Medicaid policy changes could affect a majority of American children and worsen already substantial coverage gaps. 

Boston, MA—By age 18, three in five U.S. children have enrolled in Medicaid or the Children’s Health Insurance Program (CHIP), and two in five have experienced a period of being uninsured, according to a microsimulation model developed by researchers at Harvard T.H. Chan School of Public Health. The study, the first to estimate cumulative insurance experience over the full course of childhood, highlights the broad reach of Medicaid and CHIP, programs that have recently undergone significant policy changes. 

“In July 2025, the Centers for Medicare and Medicaid Services stopped approving Section 1115 waivers for multiyear continuous public insurance eligibility among children. In the same month, the federal budget reconciliation bill was signed into law, which, according to Congressional Budget Office projections, will reduce Medicaid funding by $1 trillion and cut enrollment by 10 to 15 million people,” said corresponding author Ye Shen, a student in the Harvard PhD Program in Health Policy. “Our study provides a valuable baseline for understanding the extent to which U.S. children’s long-term insurance coverage may be affected by these sweeping changes.”

The study will be published Sept. 24, 2025, in JAMA.

Fragmented health insurance claims data and short follow-up periods in national surveys have hampered efforts to track childhood insurance coverage over long periods in the U.S. To address these limitations, the researchers combined national natality, socioeconomic, demographic, and insurance data in a microsimulation model to generate individual insurance trajectories from birth through age 18 for a nationally representative cohort of children. The researchers then estimated cumulative insurance outcomes over 18 years under policy conditions similar to those between 2015 and 2019, after the coverage expansions of the Affordable Care Act but before the temporary policies introduced during the COVID-19 public health emergency in 2020.

The study’s estimates suggest that by their 18th birthday, 61% of children have enrolled in Medicaid and CHIP, and 42% have experienced gaps in coverage. The researchers also estimated that disruptions to coverage were more common in states that did not expand their Medicaid programs. Among children born into Medicaid or CHIP coverage in non-expansion states, 59% experienced periods of being uninsured, compared to 36% of their counterparts in expansion states. When comparing Medicaid and CHIP income eligibility upper levels across states, states with the most restrictive thresholds saw the highest share of coverage disruptions among children covered in Medicaid or CHIP at birth.

“Upcoming changes to Medicaid could affect a significant portion of children and worsen already substantial insurance gaps,” said senior author Nicolas Menzies, associate professor of global health and faculty member in the Center for Health Decision Science. “We’re particularly worried about explicit loss of public insurance eligibility for noncitizen children; spillover effects through parental Medicaid coverage losses due to work requirements and more eligibility checks; and state-level cuts to Medicaid.”

Article information

“Insurance Dynamics During Childhood in the Fragmented US Health System,” Ye Shen, Benjamin D. Sommers, Laura A. Hatfield, Catherine Hayes, Ankur Panya, Nicolas A. Menzies, JAMA, September 24, 2025, doi: 10.1001/jama.2025.15488

Sommers reported receiving grants from the Commonwealth Fund, Episcopal Health Foundation, and United Hospital Fund; honoraria from Kinetix Group, Massachusetts Psychiatric Society, and American Medical Association; and travel support from the AcademyHealth outside the submitted work; and had been employed by the U.S. Department of Health and Human Services from January 2021 to July 2023. No other disclosures were reported.

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