In 1929, he stopped writing for the Manchester Guardian and began writing children's books. He wrote the Swallows & Amazons series between 1930 and 1945. They are based on his childhood holidays at Nibthwaite. In the author's preface, of 1958 he writes:
"I have often been asked how I came to write Swallows and Amazons. The answer is that it had its beginning long, long ago when, as children, my brother, my sisters and I spent most of our holidays on a farm at the south end of Coniston. We adored the place. Coming to it we used to run down to the lake, dip our hands in and wish, as if we had seen the new moon. Going away from it, we were half-drowned in tears. While away from it, as children and as grown-ups, we dreamt about it. No matter where I was, wondering about the world, I used at night to look for the North Star and, in my minds eye, could see the beloved skyline of great hills beneath it. Swallows and Amazons grew out of those old memories. I could not help writing it. It almost wrote itself. "
The books are mainly about two families of children who love to sail, fish and camp. Sailors John, Susan, Roger and Titty (it's short for Laeticia) Walker are the Swallows and pirates Nancy and Peggy Blackett are the Amazons. Each family has a beautiful little boat, and they are free to go on short adventures, so long as their parents know where they are. As they go, they imagine even greater adventures, such as traveling to the North Pole, or going on a mining expedition.