A 4-year-old child is brought to the clinic with a 4-day his…

A 4-year-old child is brought to the clinic with a 4-day history of fever, cough, runny nose, and red watery eyes. Physical examination reveals small white lesions on the buccal mucosa. Twenty-four hours later, the child develops a red maculopapular rash that begins along the hairline and behind the ears before spreading downward to the trunk and extremities. Which of the following is the most likely diagnosis?