Viral Gastroenteritis: This is the most common cause of epigastric pain and vomiting in children, often accompanied by diarrhea. The condition is highly contagious and usually self-limiting, with symptoms resolving within a few days.

Gastroesophageal Reflux Disease (GERD): Common in young children, GERD can cause epigastric pain and vomiting due to the reflux of stomach contents into the esophagus.
Constipation: Although less obvious, constipation can lead to abdominal pain and vomiting in children, as the pain can be referred to the epigastric region.
Food Poisoning: Similar to viral gastroenteritis, food poisoning from consuming contaminated food can lead to sudden onset of vomiting and epigastric pain.

Appendicitis: Although less common in very young children, appendicitis can present with epigastric pain that migrates to the right lower quadrant, and vomiting. It's a surgical emergency if not promptly treated.
Intussusception: A condition where a part of the intestine telescopes into another, leading to bowel obstruction. It's a medical emergency that can cause severe abdominal pain, vomiting, and bloody stools.
Pyloric Stenosis: Typically presents in infants but can occasionally be seen in older children, characterized by projectile vomiting after feeding due to narrowing of the pylorus.

Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis are rare in young children but can cause chronic abdominal pain, vomiting, and changes in bowel habits.
Pancreatitis: Inflammation of the pancreas, which can be caused by various factors including trauma, infections, or certain medications, leading to severe epigastric pain and vomiting.
Hepatitis: Infection or inflammation of the liver, which can cause abdominal pain, vomiting, and jaundice, although it's less common in presenting with isolated epigastric pain and vomiting.