Coverage for children under a parent's individual or group policy may extend to the child's 26th birthday. A plan that offers dependent coverage of children must make it available until age 26, and before that age it may define a dependent only by the relationship between child and parent. It may not use marital status, student status, employment, residency or financial dependency. The plan does not have to cover the child's own child.

Disabled dependents (California, §10277(a)): reaching the policy's limiting age does not end a child's coverage while the child is both: - incapable of self-sustaining employment because of a physically or mentally disabling injury, illness or condition, and - chiefly dependent on the employee or member for support. Student status, or a diagnosis alone, does not continue coverage under this rule.

Aging out and COBRA: when a child stops being a dependent under the plan's terms, for example by turning 26, that is a COBRA qualifying event. The child may continue the group coverage for up to 36 months. The 18-month period is for the employee's termination or reduced hours, not for a child aging out.