temporary guardianship minor responsible for medical care?

If you have any info about this situation please give your input. My parents had mentored an inner city child from Milwaukee, WI since he was 5 years old. He came from a drug mother and his father has never done anything for him. His birth mother has 6 other children who all belong to the state/are on welfare. He is now 15 and my family had been transfered from Wisconsin to Georgia due to a job transfer almost 2 years ago. His mom was able to sign Temporary Guardianship over to my mom (who has no relation to his family..we are white if that matters?) Since he isn't in Wisconsin anymore he cant get state medical care and since we do not have full custody of him he cant be under our family insurance. My mother took him to the dentist and his mouth was basically rotten and has been paying out of pocket for the dental expenses as well as doctor appointments for school physicals, etc. My parents are hard working middle class people and have to make payments on credit cards to cover his medical care. I have looked all over to see if we could get him coverered by the state because they are saving the state so much money due to the fact the state doesn't have to pay for his food, school,etc. He most likely would be in prison right now if my parents wouldn't have taken him out of his family situation. (One of his brothers is in prison for murder, one of his other brothers was charged for sexually assaulting his sister) (he was the typical welfare child..parents paid nothing his entire life..very sad) If anyone has information on coverage/liability of temporary guardians that would be very helpful!! All they want is coverage. Are they legally responsible if he is hurt and lets say ends up in the hospital?
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I was able to add a child to my insurance based on a "revocable permanent assignment of guardian" that I wrote up, his mom signed, and was notarized. Try doing the guardianship over only saying "this guardianship is valid unless and until revoked by me in writing". Your parents' insurance may then cover him.
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