Croup is a respiratory condition in children is caused by a parainfluenza virus. It is transmitted by airborne droplets from an infected child's cough. Here are the symptoms of croup: - A sharp, barking cough, usually accompanied by noisy and difficult breathing, and sometimes by hoarseness caused by inflamed vocal cords ( laryngitis). - Laboured breathing that seems to put strain on the neck muscles, ribs, or breastbone, consequently making these areas contract noticeably with each breath.