The only Shriver named John born into the family that has any relationship to the Kennedy's was born in 2009 - so he would be about 4 years old right now. I doubt that the pictures are of him.
Eunice Kennedy Shriver (JFK's sister) married Sargent Shriver. He had only one brother, Thomas. Sargent's sons were Mark, Anthony, Bobby and Timothy. Thomas had one son, also named Thomas.
Sorry, just another porn gimmick to sell something.