It's almost inevitable that book-loving parents will try to get their kids enthusiastic about the books they loved themselves in their youth, and that was the case with "The Adventures of Harold and the Purple Crayon" by Crockett Johnson.
I have a sharp memory of these books being in our junior school library, mostly ignored in favour of "Clifford the Big Red Dog" but they caught my eye because Harold is a kid who draws, who lets his imagination take him for a walk, and whose adventures are born from the simple linework and doodles he cooks up with the aid of the best drawing tool on the planet, the purple crayon.
Harold's adventures begin fairly simply with a journey, but soon he goes on a more magical quest to save a kingdom from a wicked witch, and even further onwards to become the star turn at a magical circus.
Johnson's genius is to keep the running theme of the crayon line as the pulse of the book, the reader is led through the story by the line and the doodles, and young readers love musing over whether Harold's purple crayon is in fact magic, and bringing the things he draws to life, or whether his imagination just takes over and the stories exist purely in his head (or on his long-suffering parents' walls!)
It's well worth seeking out the edition shown above (this is the copy we own after a fairly fruitless search, finally finding one in a secondhand book store) though there are separate stories too (this volume just collects them all together).
I also have a strong memory of an animation produced around the time the books were popular, but the magic is kinda ruined a bit when you're not the one driving the narrative with your own imagination.
Original Review Link:
The Adventures of Harold and The Purple Crayon by Crockett Johnson (HarperCollins Children's Books)