Viral Gastroenteritis: This is the most common cause of abdominal discomfort and diarrhea in children, often due to rotavirus, norovirus, or adenovirus. The symptoms typically last for a few days to a week, which aligns with the duration mentioned in the question.

Bacterial Gastroenteritis: Caused by bacteria such as Salmonella, Shigella, or E. coli, which can lead to similar symptoms. The presence of blood in the stool or a higher fever might suggest a bacterial cause.
Food Poisoning: Consuming contaminated food can lead to abdominal discomfort and diarrhea. The history of recent food intake, especially of high-risk foods, can help in diagnosing this condition.
Lactose Intolerance: In children who have recently started consuming lactose-containing products, lactose intolerance can cause abdominal discomfort, bloating, and diarrhea due to the inability to digest lactose.
Irritable Bowel Syndrome (IBS): Although less common in young children, IBS can cause chronic abdominal pain and changes in bowel habits, including diarrhea.

Appendicitis: Although it typically presents with localized right lower quadrant pain, early appendicitis can have non-specific symptoms including diarrhea. Missing this diagnosis can lead to severe consequences.
Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause abdominal pain, vomiting, and bloody stools. It's a medical emergency that requires prompt diagnosis and treatment.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can present with chronic diarrhea, abdominal pain, and weight loss. Early diagnosis is crucial for effective management.
Intestinal Obstruction: Can cause severe abdominal pain, vomiting, and diarrhea. It's a surgical emergency that requires immediate attention.

Celiac Disease: An autoimmune reaction to gluten that can cause chronic diarrhea, abdominal pain, and malabsorption. It's less common but should be considered in children with persistent symptoms.
Giardiasis: An intestinal infection caused by the Giardia parasite, which can lead to chronic diarrhea, abdominal cramps, and weight loss.
Tropical Sprue: A rare condition that affects the small intestine's ability to absorb nutrients, leading to chronic diarrhea and malabsorption. It's more common in tropical regions.
Whipple's Disease: A rare, systemic bacterial infection that can cause chronic diarrhea, abdominal pain, and malabsorption, among other symptoms.