Two birthdays...no years of birth. Karen Wallace is a Canadian-born English author of fiction and non-fiction books. She is most popular in my library for her four dinosaur picture books: I am an Anklosaurus; I am a Quetzalcoatlus etc and her readers about Sherlock Hound. The children are always disappointed when they realise that they have read them all and that there aren't any more. Personally I really like the books she did for the Read and Wonder series ... My Hen is Dancing; Think of an Eel; Bears in the Forest and Gentle Giant Octopus.
In fact when I looked on the library catalogue I began to think Karen Wallace is a prolific writer, we have so many books of hers!
In comparison, American Tad Hills has many fewer books in our library, but we would have most of those he has authored and illustrated, including his newest How Rocket Learned to Read which is a big hit with children learning to read. We have toys to accompany the Duck and Goose titles so those books are always out being enjoyed at someone's house.