One Boy by Laura Vaccaro Seeger

From chapters.ca:
One Boy is a perfect example of why Kirkus Reviews calls Laura Vaccaro Seeger the "emerging master of the concept book" - a die- cut book exploring counting and words- within- words, "and" the power of art and imagination. At the start, readers see a sad boy surrounded by empty, lonely chairs. At his feet is a bag with paint brushes peeking out. The text reads "ONE boy" which - with a turn of the page and a look through a cleverly cut hole - turns into "all alONE." Page after page, the book becomes populated with seals, apes, and monkeys, all examples of words- within- words. Finally, we come back to "ONE boy" who is "all dONE," and we discover where all the characters came from.