Dr Phil: What can I do to ensure my two-year-old doesn't get croup?

"Croup is a condition in which the vocal cords become swollen due to viral infection. This can cause a distinctive, seal-like barking cough."

Pic: iStock

My two-year-old son has asthma and often gets croup. I find steaming works best to open the airwaves. 

Can I do anything to ensure he does not develop croup in the first place? Is he more at risk of getting whooping cough because he is asthmatic?