RSV
RSV, or respiratory syncytial virus, is the leading cause of bronchitis in children and initially resembles the common flu. A cough, running nose, and fever are typically exhibited, and children will sometimes develop wheezing. It can be hard to identify initially but is on average much milder when contracted by older children and adults.
http://www.indiancrestpeds.com/pediatrics/westminster-pediatrics-treat-four-common-childhood-illnesses/