Yoko's first known child, Kyoko Cox, was born on August 8 of 1963. Sean Lennon was born (induced, according to some sources) on October 9 of 1975.

Before her involvement with Tony Cox, Ono had a sexual relationship with a young writer named Michael Rumaker. Rumaker published book, The Butterfly, about this relationship in 1962. He gave Yoko the pseudonym Eiko, and noted that she had a "scar on her belly, a tough ridge of purple flesh," which he believed was the mark of a caesarian birth

In the late 70s, the Lennons were friends with a woman named Marnie Hair. Hair remembered Ono saying to her: "All of my children were born by caesarian." Not "both" but "all."

In the early 1960s, Ono left Michael Rumaker (without a word of explanation -- a painful experience Rumaker describes in The Butterfly) for LaMonte Young. Young already had a girlfriend, a poet named Diane Wakoski. Wakoski recalled Ono telling her that she had a child in Japan. At the time of her affair with LaMonte Young, Ono was living with a writer named Erica Abeel. Abeel has since written about the bizarre experience of living with Ono on her memoir Wild Girls. Ono is given the psudonym Rinko Park. Abeel describes coming home to find Yoko/Rinko having sex with "LaMonte Young of the greasy ponytail" in her (Abeel's) bed. "He was dirty and greasy. I washed the pillowcase.") Abeel recalls Ono telling her that she had a baby in Japan. Ono boasted to Abeel that she had composed an opera. This alleged composition was for vocals only, and Ono stated that the purpose of her vocals was to make clear the pain of child-bearing.

All of this predated Tony Cox' first meeting with Ono in the Japanese mental institution into which Ono's family had placed her.