Depends on what state they are living in.
Pennsylvania. WE have a governor with no backbone.
Yeah that's true. Medicaid although funded with federal funds is a state ran program. In some states the County Health Departments do inoculations. IIRC when I was a kid our doctor told my parents to take me there because they would keep the records the school would need. That was over 50 years ago though and on the heels of the nation recovering from the Polio epidemic. Dad had insurance.
At a minimum and this is a guess in this case it may be simply the baby is placed on Medicaid but not the parents. Some states do that. Another thing to look for is groups who run health care clinics at greatly reduced price or on ability to pay.