A 3-year-old child is brought to the GP with a 2-day history of fever, sore throat, and a rash. On examination, the temperature is 38.9°C. The pharynx is erythematous with exudates, and there are tender anterior cervical lymph nodes. A widespread, fine, erythematous, punctate rash is noted, feeling like sandpaper, particularly prominent in skin folds. The tongue has a white coating with prominent red papillae ('strawberry tongue'). What is the most likely diagnosis?