A child with painful mouth sores and fever is likely suffering from which condition?

Hand, foot, and mouth disease is a common viral illness typically caused by coxsackievirus, particularly in young children. It is characterized by distinct symptoms, including painful mouth sores, fever, and a rash on the hands and feet. The presentation of painful mouth sores accompanied by fever aligns with what is often seen in this condition.

In contrast, herpes simplex infection usually results in painful vesicular lesions primarily around the oral cavity and is often localized rather than associated with widespread symptoms like fever in children. Varicella, also known as chickenpox, presents with a generalized vesicular rash along with fever, but the characteristic mouth sores are not a primary symptom. Secondary syphilis can present with a variety of systemic symptoms but is less likely to cause isolated painful mouth sores and fever in the presentation typical of younger children.

Thus, when considering the combination of painful mouth sores and fever, hand, foot, and mouth disease emerges as the most fitting diagnosis given its well-established clinical presentation in pediatric populations.