It looks like your family may qualify for Medicaid or CHIP.
If you already have Medicare coverage, you don't need to purchase a health plan here. You're considered covered.
CHIP is a program that provides low-cost health coverage to children in families that earn too much money to qualify for Medicaid.
For more information about CHIP, visit https://www.healthcare.gov/medicaid-chip/.
Children who qualify for CHIP cannot purchase a plan with a tax credit.