Catherine Porter, of Sotheby's, who organised the sale which has taken a year to put together, said the books belonged mainly to two collections.
"I think it is probably the greatest sale of children's books ever," she said. "All the classics are there with very few exceptions, and there has never been a sale like it."
The most expensive book in the auction is a first edition of Beatrix Potter's The Tale of Peter Rabbit, which is expected to fetch up to pounds 30,000.
Potter first created Peter in a letter to the son of her former governess. A few years later when she wanted to publish the story she received several rejections from Frederick Warne and finally decided to issue the book herself. Only 250 copies were made and were mainly given to friends and family.
This 1901 copy is inscribed to Mary Hutton, a cousin of Potter. It was while staying with them that the author first heard the story of a tailor in Gloucester who left a waistcoat out in his shop over the weekend and returned to find it had been finished, apart from one buttonhole. That, of course, was her second book, which was also privately published.
Miss Porter said the most exciting lot was an extremely rare first edition of The Wind in the Willows, still in the all-important dust jacket. Only three other copies have appeared at auction in the past 25 years and it is expected to sell for pounds 15,000.
"It is so rare to find one with the cover intact. Most people just took them off and threw them away and it is only recently that they have been considered important," she said.
The sale also includes a copy of JM Barrie's Peter and Wendy, the sequel to Peter Pan, which is believed to be the only copy signed by the author, as well as the only signed copy of Rudyard Kipling's Just So Stories, which was presented to his mother's best friend.