Keeping won two Kate Greenaway Medals from the Library Association for the best children's book illustration of the year, for his own story Charley, Charlotte and the Golden Canary (1967) and for a new edition (1981) of Alfred Noyes's poem "The Highwayman".

[1][2] For the 50th anniversary of the Medal (1955–2005), a panel named his edition of The Highwayman one of the top ten winning works, which composed the ballot for a public election of the nation's favourite.

36 He attended the Frank Bryant School for Boys in Kennington, North London,[8] leaving at the minimum age of 14, after which two of his aunts paid for him to take a correspondence course in art.

37 He returned to civilian life in 1946 with a profound depression and a belief that a head wound he had sustained had disfigured him on the inside as well as (temporarily) on the outside, and would cause him to turn evil like Dr Jekyll becoming Mr Hyde.

[9] He also worked as a life model, and on one such occasion in 1949 his demonstration of the functions of the muscles of the back attracted the eye of Renate Meyer, a fellow student who had left Germany with her family in 1933.

52, 54 In 1956 he began to work through the artist's agent B. L. Kearley Ltd, whose rep Patsy Lambe referred him to Mabel George, editor of children's books at Oxford University Press.

He was unenthused by the ancient Roman subject matter, but experimented with double page spreads and drawings in the margins, and was quickly assigned more books by Sutcliff and others,[6]: 51–55 [11] including Henry Treece.

38  Keeping, along with Victor Ambrus, established a new, exuberant style of illustration for children's historical fiction,[7]: p. 40  refusing to shy away from the violence of warfare.

[12] Leon Garfield and Edward Blishen's retelling of Greek myths, The God Beneath the Sea, which Keeping illustrated in 1970, won the Carnegie Medal for that year.

From the later 1960s Keeping, alongside illustrators like Brian Wildsmith and John Burningham, took advantage of advances in printing technology to move from black and white work to adventurous colour techniques.

The full-colour illustrations are messy and spontaneous, using intense colour, sponge texturing and wax resist, and won Keeping his first Greenaway Medal.

Keeping continued to produce colour picture books from time to time, including Railway Passage, which was Highly Commended for the 1974 Greenaway Medal;[15][a] Sammy Streetsinger (1984), about a subway busker's rise to fame as a pop star and subsequent return to happy obscurity; and his final book, Adam and Paradise Island, another story of the changing landscape of London, which was published posthumously in 1989.

For the same publisher he illustrated Ghost Stories of M. R. James (1973), Horace Walpole's The Castle of Otranto (1976) and Victor Hugo's Les Misérables (2 volumes, 1976) in two-colour lithographs, and Fyodor Dostoyevsky's The Idiot (1971) in line drawings.[6]: pp.

82 In 1975 Keeping produced perhaps his most personal work, Cockney Ding Dong, a lavish 190-page volume collecting and illustrating the traditional songs of the family singalongs of his childhood.

155–157  His biographer has commented, His formidable originality within the picture-book convention may not have been altogether apparent to Keeping himself, which is both a strength and a weakness: the strength that he could communicate with unrivalled emotional intensity - but possibly only with one child in twenty; the concomitant weakness is that there was not a lot he could do to broaden this minority appeal and ensure that his books remained in print over longer periods.Keeping's former editor Mabel George said of him, "I have always had a strong feeling that Charles was a true genius... it is my belief that he came to maturity very slowly (not in terms of technique, at which he was a master from his earliest days) but from the point of view of his self-confidence as an artist.

... he was all the time growing and developing as a man whose whole life, heart and mind, was dedicated to exploring the human situation in a universe that he found both beautiful and terrifying."[6]: p.