This is described as a rambling, handwritten note signed "John Lennon" actually written by his cousin Marilyn McCabe to Oral Roberts in the early 1970s, as quoted in Oral Roberts : An American Life - 1985 by David Edwin Harrell, p. 310. It was later published in full as if it were actually written by Lennon in How to be a Successful Teenager - 1994 by Rick Jones, Ch. 5 : The Secret About Material Things, p. 54.
Quoted as a 1968 statement of Lennon's in Sunday Tasmanian - 29 September 1996, and in The Rough Guide to the Beatles - 2003 by Chris Ingham This actually derives from a statement which Lennon perhaps had been quoting: Were art to redeem man, it could do so only by saving him from the seriousness of life and restoring him to an unexpected boyishness. José Ortega y Gasset, in "Art a Thing of No Consequence" in The Dehumanization of Art - 1925.
I know you understand the little child inside of your man.
Double Fantasy - 1980 - "Woman".