He was married twice and had a son from each marriage. Cynthia was already pregnant when they got married in 1962 at a registry office. The son was named Julian, after John's deceased mother Julia. Julian had a few musical hits but nowhere near the success of his father. He now produces/directs movies and campaigns for the protection of the environment. He and John were not terribly close. John and Yoko Ono were married in 1969. Yoko gave birth to Sean in 1975, after a few miscarriages. I think she was confined to bed for much of her pregnancy. There have been some claims by people that they were an illegitimate child of John Lennon, none of them substantiated. I know that Paul has a son from before his marriages however.