Which virus is the leading cause of the croup syndrome in young children and, when infecting mammalian cells in culture, will hem absorb red blood cells?

Parainfluenza viruses are important causes of respiratory diseases in infants and young children. The spectrum of disease caused by these viruses ranges from a mild febrile cold to croup, bronchiolitis, and pneumonia. Parainfluenza viruses contain RNA in a nucleocapsid encased within an envelope derived from the host cell membrane. Infected mammalian cell culture will hem absorb red blood cells owing to viral hemagglutinin on the surface of the cell.