Viral Gastroenteritis: This is the most common cause of acute diarrhea in children, often caused by rotavirus, norovirus, or adenovirus. The sudden onset of diarrhea, possibly accompanied by vomiting, fever, and abdominal cramps, is typical.

Bacterial Gastroenteritis: Caused by bacteria such as E. coli, Salmonella, or Shigella, which can lead to diarrhea, often with blood and mucus, fever, and abdominal pain.
Food Poisoning: Consuming contaminated food can lead to diarrhea, vomiting, and stomach cramps. The onset is usually rapid.
Lactose Intolerance: Inability to digest lactose, leading to bloating, gas, diarrhea, and stomach cramps after consuming lactose-containing products.
Antibiotic-Associated Diarrhea: Diarrhea that occurs during or after antibiotic use, which can disrupt the normal gut flora.

Intussusception: A condition where a part of the intestine slides into an adjacent part, potentially cutting off blood flow. It's a medical emergency and can present with sudden onset of abdominal pain, vomiting, and bloody stools.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic diarrhea, abdominal pain, weight loss, and blood in stool.
HUS (Hemolytic Uremic Syndrome): A potentially life-threatening condition that can follow certain bacterial infections (like E. coli O157:H7), leading to kidney failure and characterized by diarrhea, anemia, and thrombocytopenia.

Celiac Disease: An autoimmune disorder where the ingestion of gluten leads to damage in the small intestine, causing diarrhea, abdominal pain, and malabsorption.
Giardiasis: An intestinal infection caused by the parasite Giardia lamblia, leading to diarrhea, abdominal cramps, and weight loss.
Toddler's Diarrhea: A condition of chronic diarrhea in toddlers, often related to diet or an immature gut.
Congenital or Acquired Immunodeficiency: Conditions that impair the immune system, making children more susceptible to infections, including those causing diarrhea.