Lennon wanted to see their son, Sean, before the boy went to sleep in their New York apartment, Ono said in Sunday's edition of "Desert Island Discs" on Radio 4.
"It was like he wasn't sure if we would get home before (Sean) went to sleep and he was concerned about that," Ono said. "That was the last thing he said, that he wanted to see Sean."
Ono, 74, said her mission is protecting Lennon's memory, but she doesn't want her children -- Sean, and Kyoko Chan Cox, her daughter from her marriage to jazz musician Anthony Cox -- to do the same for her, the Sunday Telegraph reported.
"After John's passing it was my pleasure actually to keep on protecting his work and I cherish the fact that I feel that I did my best," she said.
Still, she said she doesn't want her children defending her memory.
"(Don't) even think about the past or your mother because your mother had a great life and you should know that," she said.