Everyone Poops (1977) written by Taro Gomi

Everyone Poops is essentially plotless. The first sixteen pages contain various prompts regarding defecation in animals such as opposites ("An elephant makes a big poop" and "a mouse makes a tiny poop"), comparisons (that various species produce various sizes and shapes of poop) and questions ("What does whale poop look like?"). 
 
On the seventeenth page, a nameless boy with black overalls and a red shirt is introduced, seen running into a bathroom. The book then goes on to explain how people of all ages, from adult to very young child, defecate, and how infants may use diapers. After that, there are only three more illustrations that lack the nameless overall-clad boy. The next page of the book, in which the child uses toilet paper and flushes the toilet, refers to the boy as "He", the only time in the story when the child is referred to as a singular entity (other accompanying images denote children in general, even though only the boy is shown). The final portion of the book explains that because every animal eats, they must therefore defecate, and the book ends with rear views of the boy and six different animals defecating and the words "Everyone Poops".