Roald Dahl had a habit of reusing his stories, changing their format slightly on the re-telling.
Danny was first published in Dahl's book Kiss Kiss (for adults) as The Champion of the World. The story is almost identical to Danny, the Champion of the World, but in this version the protagonists are two men, Claud and Gordon. When Dahl first moved to Buckinghamshire he met a local man called Claude who taught him about the countryside and poaching, particularly poaching trout. Dahl used his own experiences with Claude as the basis for this story.
In Danny, the Champion of the World, Danny's father tells him the story of the Big Friendly Giant. In 1982 he published The BFG, making the protagonist of the story a little girl called Sophie, based on his own grand-daughter.