Viral Infection: This is the most common cause of fever in toddlers, often due to viral upper respiratory tract infections. The lack of specific symptoms is typical in the early stages of many viral infections.

Ear Infection (Otitis Media): Toddlers are prone to ear infections, which can present with fever as the only initial symptom, especially if the child is too young to complain of ear pain.
Urinary Tract Infection (UTI): UTIs can cause fever without other obvious symptoms in young children, making them an important consideration.
Roseola: A common viral illness in toddlers characterized by high fever followed by a rash, but the rash may not be present initially.

Meningitis: Although less common, meningitis is a life-threatening condition that can initially present with fever alone. Early recognition is crucial for effective treatment.
Sepsis: Bacterial sepsis can cause fever without specific symptoms and is a medical emergency.
Pneumonia: Can present with fever and minimal or no respiratory symptoms in young children, especially if it's a viral pneumonia or in the early stages.

Kawasaki Disease: An acute febrile illness of childhood that can present with fever without other symptoms initially. It's rare but important to consider due to its potential for cardiac complications.
Juvenile Idiopathic Arthritis (JIA): Systemic JIA can present with fever of unknown origin, although it's less common in toddlers.
Lymphoma or Leukemia: Although very rare, these conditions can cause prolonged fever without other specific symptoms in children.