Adopted foster children qualify for Medicaid. Once the adoption is finalized, you will put your child on your insurance with MC as a secondary. MC will pick up co-pays and meds plus anything that your insurance doesn't pay for. I know they pay for some OTC medications.
Check out your state adoption subsidies at
http://www.nacac.org/subsidy_stateprofiles.html
It'll show you what your state pays for.