You can add your children to your marketplace plan, but because they are eligible for your state’s Children’s Health Insurance Program (CHIP), they are not eligible for premium tax credits. The exception to that is if you live in a state that has a waiting period for enrolling in CHIP. During the waiting period, your children are eligible for a premium tax credit; when the waiting period has ended and they can enroll in CHIP, your children will become ineligible for the tax credit. (26 C.F.R. § 1.36B-2(c)).