STAMFORD - School nurses and doctors say more kids than usual are coming down with "croup," which can cause difficulty breathing.Since the symptoms are similar to asthma, doctors are urging parents to learn how the ailments differ. Doctors say that a "barking cough" is the telltale sign of croup, as opposed to the difficulty breathing that comes with asthma.Croup is a virus that usually runs its course with treatment of symptoms. Dr. Maher Madhoun says to call a pediatrician if the symptoms of croup persist.