Viral Exanthem (e.g., Roseola, Measles, Chickenpox): This is often the most common cause of rash and fever in children, with the addition of cough suggesting a viral respiratory component. The rash, fever, and cough can be part of the initial presentation of these illnesses.

Pneumonia: Can cause fever, cough, and in some cases, a rash if it's a specific type like pneumococcal pneumonia. Abdominal and back pain can be referred pain from the chest.
Influenza: Especially during flu season, can present with fever, cough, and body aches, including abdominal and back pain. A rash is less common but can occur.
Urinary Tract Infection (UTI): Can cause abdominal pain, fever, and in some cases, a rash if there's an associated allergic reaction or if the infection spreads. Cough is less common but can occur with severe infections.
Gastroenteritis: Can cause abdominal pain, fever, and sometimes a rash if there's an allergic component to the illness. Cough is less common but can occur with certain viral causes.

Meningitis: Although less common, meningitis can present with fever, rash (in the case of meningococcal meningitis), and severe headache or neck stiffness, which might be referred to as back pain. It's critical to identify and treat promptly.
Kawasaki Disease: An acute febrile illness that can cause rash, fever, cough, and abdominal pain. It's a leading cause of acquired heart disease in children, making prompt diagnosis crucial.
Septicemia: Bacterial infections in the blood can cause fever, rash, and a wide range of other symptoms including abdominal and back pain. Early recognition and treatment are vital.
Pneumococcal Sepsis: Similar to septicemia, pneumococcal sepsis can present with fever, cough, rash, and severe illness, requiring immediate medical attention.

Juvenile Idiopathic Arthritis (JIA): Can cause fever, rash, and joint pain, which might be perceived as abdominal or back pain. It's less common but should be considered in the differential for chronic symptoms.
Lyme Disease: In endemic areas, can cause a distinctive rash (erythema migrans), fever, and in some cases, abdominal or back pain if there's involvement of the joints or nervous system.
Rocky Mountain Spotted Fever (RMSF): A tick-borne illness that can cause fever, rash, and severe headache or abdominal pain. It's rare but potentially deadly if not treated promptly.
Leptospirosis: A bacterial infection that can cause fever, rash, and a wide range of symptoms including abdominal and back pain. It's more common in certain geographic areas or after exposure to contaminated water.