Barbara Cooney is a well known American author/illustrator who won the Caldecott Medal twice, for The Ox Cart Man and for Chanticleer and the Fox. My favourite of her books is The Year of the Perfect Christmas Tree which was written by Gloria Houston and illustrated by Barbara. This book expresses the true sentiments of Christmas and puts it in a context quite foreign to the children I teach, but this does not matter, as the children sit spellbound through the reading, in awe of Ruthie's courage and quest to honour her family tradition. It is in the same must-read Christmas category as Susan Wojciechowski and P.J. Lynch's The Christmas Miracle of Jonathan Toomey.
Frank Asch is 'famous' in my library for his series of books about Moonbear. (See Happy Birthday Moon among others). They are perfect for 3 to 6 year olds. He has big ideas, adventures and a friend, all the things children of that age want. Of course he has written and illustrated other books, but it is hard to go past these beauties. The stories are on Youtube and his website has activities to keep children busy. Once you have exhausted Moonbear, read his books about the sun, water and wind: The Sun is my Favourite Star; Water; and Like a Windy Day.