Toddler Diarrhea? There's no such thing. Its not normal for your 3 year old to be incapable of producing a formed stool.
Constipation? Not normal. Babies and children should be eliminating multiple times per day.
When Dominic was a newborn, everyone told me it was perfectly normal for him to only poop one day a week. Granted, that day, he went throught A LOT of diapers. Its not normal.
He had one of the worst every diaper rashes we'd ever seen. It was yeast. It was cracked and bleeding. No one told me that cracked and bleeding on the outside meant cracked and bleeding onh the inside. No one told me that I could see the ACID eating through his skin with every bowel movement - that the same acid was also eating through his gut. It took years and a stool test by the DAN doctor to confirm red blood cells in his stool - indicative of leaky gut syndrome.