It Hurts When I Poop! A Story for Children Who are Scared to Use the Potty was written by Howard J. Bennett, a clinical professor of pediatrics at the George Washington University School of Medicine. The book is published by the American Psychological Association under the Magination imprint.
While this book wont be for everyone (it is, after all, about a very specific problem), I can see that it would be a lifesaver for a parent dealing with the issue in question. It is nicely and clearly written (and not at all in a pedantic manner or in a way that puts kids down) and the illustrations work well.
In the story, we meet Ryan, who loves dinosaurs, but hates to take a poop. He does everything he can to avoid it and gives himself tummy aches. When his parents take him to the doctor, the doctor tells him a story about a character named Bill who had a messy house. She explains to Ryan that we have to take care of our tummies and pay attention to what goes in them (some foods causing soft poops and other foods causing hard ones).
The end of the book gives general tips for parents and kids about good eating habits for digestive health and could help parents create their own poop programs for their kids.
The book is intended for children aged 3 to 6 and would definitely be a huge help in a family with a child with Ryans problem. Id definitely recommend this one to parents and kids who need it. Heck, I learned a few things reading it.