My MIL left my kids in the car at the store: Advice?

sorry for a long post but, last week my mother-in-law left my 2 children age 6 and 1 in a car in a car park while she went into a supermarket (the car was locked) its always busy in the supermarket so its not the case of “nipping in” a man found my children in the car and stayed with them asking where the mam and dad was and my oldest said his nanny is in the shop getting nappies, the man asked if the children are okay and stayed until my mother inlaw came back. he had taken a photo of my kids a