Viral Gastroenteritis: This is the most common cause of vomiting and diarrhea in children, often due to rotavirus, norovirus, or adenovirus, and typically presents without fever in the early stages.

Food Poisoning: Bacterial or viral contamination of food can cause similar symptoms, and the lack of fever does not rule out this possibility, especially if the child has consumed undercooked or spoiled food.
Lactose Intolerance or Milk Protein Allergy: These conditions can cause gastrointestinal symptoms in children, including vomiting and diarrhea, after the consumption of lactose-containing or milk protein-containing products.
Infectious Gastroenteritis due to Bacteria: While less common than viral causes, bacterial infections like Salmonella or E. coli can cause vomiting and diarrhea, sometimes without an initial fever.

Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause intermittent abdominal pain, vomiting, and sometimes diarrhea. It's a surgical emergency.
Appendicitis: Although less common in very young children, appendicitis can present with vomiting and diarrhea, and it requires prompt surgical intervention.
Pyloric Stenosis: A condition where the pylorus (the passage between the stomach and small intestine) thickens, causing projectile vomiting. It's more common in infants but can occur in toddlers.

Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis are rare in young children but can cause chronic diarrhea, vomiting, and other gastrointestinal symptoms.
Celiac Disease: An autoimmune reaction to gluten, leading to small intestine damage and causing diarrhea, vomiting, and malabsorption.
Congenital or Acquired Intestinal Obstruction: Conditions such as atresias or volvulus can cause vomiting and diarrhea due to a physical blockage in the intestines.