Devastated!!! My four and half year old saw a clip of at a neighbor's house. I am completely devastated!?

My four and half year old and I were visiting a neighbor. while I was talking with my neighbor the kids were playing in the basement. My neighbor's 7 year old unknowingly order a o from ON Demand. My son and neighbor's four and half year both saw a very explicit scene. One of the daugthers ran up to say something inappropriate was on tv. I am mortified!!!! I am sick to my stomach about this. I have spoken to my son and told him what he saw was inappropriate. I monitor his tv watching which is limited to begin with. He watched Noggin and the Disney channel. I feel my son's innocence has been scared and I do not know what to do. Has anyone been experienced this and how did you handle this. My husband and I have talked to our son that our bodies are private and our private areas are private...that is why we wear clothes. Please any advice is welcomed. thank you...I am sick over this!