Proper title: "For Johnny", written by John Pudney in 1942.

"Johnny head-in-air" was indeed a reference to the famous children's poem quoted above. This poem, titled "Die Geschichte vom Hans Guck-in-die-Luft", was part of a set of poems called Struwwelpeter (Shock-headed Peter), cautionary tales which the psychologist Heinrich Hoffman wrote for his three-year-old son.