Unfortunately, you haven't provided a specific question or symptoms for an 8-year-old. However, I can guide you through a general approach to differential diagnosis using the categories you've specified. Let's consider a hypothetical scenario where the question involves a child presenting with abdominal pain, as this is a common and broad symptom that can lead to various diagnoses.

Single Most Likely Diagnosis

• Constipation: This is a common issue in children, often presenting with abdominal pain, changes in bowel habits, and sometimes vomiting. It's frequently seen in pediatric practice and can be diagnosed based on history and physical examination.

Other Likely Diagnoses

• Viral Gastroenteritis: This condition is characterized by inflammation of the stomach and intestines, usually due to a viral infection. Symptoms include diarrhea, vomiting, abdominal pain, and fever. It's a common cause of abdominal pain in children.
• Urinary Tract Infection (UTI): UTIs can cause abdominal pain, especially in the lower abdomen, and are accompanied by symptoms like dysuria, frequency, and fever. They are more common in girls.
• Appendicitis: Although less common in younger children, appendicitis is a significant cause of abdominal pain that requires prompt surgical intervention. Symptoms can include pain that initially is diffuse or around the navel and then localizes to the lower right abdomen.

Do Not Miss Diagnoses

• Intussusception: A condition where a part of the intestine slides into an adjacent part, potentially cutting off blood flow. It's an emergency and presents with severe abdominal pain, vomiting, and sometimes bloody stools.
• Pneumonia: Abdominal pain can be a referred pain from a lower lobe pneumonia, especially in younger children. Symptoms might also include fever, cough, and difficulty breathing.
• Diabetic Ketoacidosis (DKA): Presents with abdominal pain, vomiting, and can lead to severe dehydration and electrolyte imbalances. It's crucial to consider in children with new-onset diabetes.

Rare Diagnoses

• Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can present with chronic abdominal pain, diarrhea, weight loss, and sometimes blood in the stool.
• Henoch-Schönlein Purpura (HSP): A form of vasculitis that can cause abdominal pain, rash, joint pain, and sometimes kidney involvement.
• Abdominal Malignancies: Though very rare in children, tumors like neuroblastoma or Wilms tumor can cause abdominal pain and a palpable mass.

This approach can be tailored to the specific symptoms and history provided for the child in question. Each diagnosis should be considered based on the likelihood, severity, and potential impact on the child's health.