My OCD completionist tendencies have driven me to add this, the earliest book I can remember. My Dad read it to me at bedtime, when I was a small child in the early 1970s. We also had a few sequels. Googling around for them, I'm delighted to realize that I recognize the titles, covers, and illustrations. Amazing what is retained in the old noggin.
Paperback, 32 pages
Published April 13, 1970 by Hodder & Stoughton General Division.