Complex sentence: Heinlein got the idea for the novel when he and his wife had some brainstorming one evening in 1948, and she suggested a new version of Rudyard Kipling's "The Jungle Book", where a human child is raised by Martians instead of wolves.
Split into simpler sentences: Heinlein got the idea for the novel when he and his wife were brainstorming one evening in 1948. She suggested a new version of Rudyard Kipling's "The Jungle Book", but with a child raised by Martians instead of wolves.