Private school day care

Hello sir/ mam, My 3 and a half years old son goes to day care as we are working parents. Since summer vacation in schools has started so the day care has launched summer camp. They insist us on paying advance money. Last Thursday they gave a message in what's app. Reach school sharp at 9:30 am there is a trip to birla planetarium. We dropped our son at 9:15 and left to office. Later the photos started coming in what's app she took all the kids at 11:30 am. From 11:30 till 1pm all the kids were made to play in sun or sit under tree. She gave lunch under a tree like a picnic. It was 40 to 42 degree temperature that day. My son returned home at 3pm that day instead of 12 noon. He was fully exhausted, hungry, burned in sun. His body was full of severe rashes from head toe. He had sunstroke. Vomited. And had high fever. Full 1 week he suffered. The rashes were so sever that he was not able to open mouth out of pain, skin pealed out. Just on butter milk and juice he survived one week. Our life became hell visiting doctors and miserably watching him suffer, just by trusting that lady sugar coated words. When i called her for an explanation she said you son is too sensitive. We will not take him hear after. By saying so is her accountability over? What legal action can I take against her and what are the chances to succeed. She even refused to pay our advance back saying they don't have a refund policy. She never gave any bill for payment. But I have online payment account statement. Plz suggest steps that can be taken. As it's ont only for my kids there are so many else who can get into this trap and suffer. Thanx.