Frog and Toad are Friends, by Arnold Lobel, HarperCollins, 1970.
It it hard to imagine a better book for emergent readers than a Frog and Toad book. The stories are short. And funny. And quirky. And easy to read. And easy to understand. And all the stories fit together to form a larger story. And Frog and Toad both have such well-formed personalities. And the illustrations are perfection. And who wouldn't want to sleep until half past May?