Normal variation in stool color: Green poo can be a normal variation in stool color, especially in toddlers who are breastfed or have a diet rich in green vegetables. The color change is usually harmless and resolves on its own.

Gastroenteritis: Viral or bacterial infections can cause green, watery stools in toddlers. Symptoms such as fever, vomiting, and abdominal pain often accompany gastroenteritis.
Dietary factors: Consuming foods or drinks with green food coloring, such as green Kool-Aid or green Jell-O, can temporarily turn stool green.
Intestinal malabsorption: Conditions like celiac disease or lactose intolerance can lead to malabsorption of nutrients, resulting in green, frothy stools.

Intussusception: A serious condition where a part of the intestine telescopes into another, causing bowel obstruction. Green, bloody stools can be a sign of intussusception, which requires immediate medical attention.
Inflammatory bowel disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause green, bloody stools, abdominal pain, and weight loss.
Bacterial infections: Certain bacterial infections, such as Salmonella or E. coli, can cause green, watery stools, and may lead to life-threatening complications if left untreated.

Biliary atresia: A rare congenital condition where the bile ducts are blocked, causing green, clay-like stools.
Alagille syndrome: A genetic disorder that affects the liver, heart, and other organs, causing green, frothy stools, and other systemic symptoms.
Congenital infections: Certain congenital infections, such as congenital syphilis, can cause green, watery stools, although this is extremely rare.