You don't need an excuse like Alan Alexander Milne's birthday to read Winnie-the-Pooh! You could do it any day just because you want to. Similarly you don't need an excuse to read his poetry. The children at school love it when I recite Missing or parts of Disobedience or Rice Pudding.
A.A. Milne was already a writer, when his son Christopher Robin was born in 1920. In 1924 he published a book of verse called When We Were Very Young. Included in this collection was a poem about a teddy bear, the first reference to Winnie-the-Pooh. Milne went on to write a book about this bear, other toys and a boy with the same name as his son. Winnie-the-Pooh was published in 1926 and another book about them and another book of verse followed later. The characters in the Pooh stories were inspired by stuffed toys of Christopher's. These original toys can be seen in the Children's Room in the New York Library. I have seen them. They look sad, as if they are waiting for Christopher to return and play with them. I also think it is because they belong in England amongst original artwork by Ernest Shepherd and early editions of the books. They would then not look out of place.
Milne's widow sold the book rights to Disney and that is why when you see Winnie-the-Pooh these days in picture book versions of the stories, he is more likely to be a very golden colour with a red jacket than to look like the loveable gentle creatures that Ernest Shepherd created.
Another English author, but with a completely different oeuvre is Raymond Briggs. For me he is the original graphic novelist. The children in my library know his work because of The Snowman and Father Christmas in both book and video format. Both get used extensively in the lead up to Christmas. Jim and the Beanstalk, a fractured version of Jack and the Beanstalk is also well-borrowed.
Catherine Anholt, also English, is the author illustrator with her husband, Laurence of the picture books about those mischievous chimpanzees, Chimp and Zee among other wonderful books for preschoolers.