My Child Is 4 Year 8 Month. He Is Facing

My child is 4 year 8 month. He is facing cough nonstop last 22 days. Doctor said nebulize with duolin every 4 hours continue 7 days. He is also said it is croup digest.
1=What is croup digest.
2= My only concern now is will these steroid duolin inhalers tamper his growth and immunity and will he get used to it all his life and will have to continue it

Please help me