Hi Lisa,
Constipation, holding, and resulting encopresis (stool leakage) are actually pretty common issues with young kids. Encopresis occurs in 1-2% of children under 10 in the U.S. It can become a big lingering problem too. Unfortunately, no one wants to talk about how their child poops their pants. As a result it, often remains a hidden shameful topic for some families.
I'm going to offer you a few resources that might help.
"Stress-free Potty Training: A common sense Guide to the right approach for your child." What's so special about this book is that it discusses 5 different common childhood temperaments and how each can effect potty training. Then they offer insights into problems and solutions for each. So different approaches for sensory kids vs assertive do it my way kids. etc.
Next is "The Ins and Outs of Poop" And "Softy the Poop: Helping families talk about Poop. Both by Thomas Duhamal. Lots of help in these two books. We also used "Everyone Poops," by Taro Gomi.
"The Kadin Method for Parenting the Defiant Child" is also a great source for teaching how to use positive reinforcement when you need a behavior change. His techniques are very positive, very joyful, and very effective.
Thank you for sharing this with readers. Parents need to know they are not alone when they encounter this challenge.
Good luck!