Child injury - grass hurting his arm

My 5 year-old child injured his arm when he was in the park. He was playing on the seesaw when it broke down and he felt on the grass hurting his arm and head. I would like to admit that my son has normal weight and for sure he was using the seesow in a proper way. Please, advice me if there is possiblity to get some money because of faulty equipment on the adventure playground. What is the responsible institution for the park's adventure playgrounds?