my son is 3.5 years old & had his first croup attack when he was 11 months old & was in hosp for 3 days - Croup to my knowledge is very contagious - however as it has been explained to me - croup is a virus - not all children that come into contact with the croup virus itself will contract the croup bug - they may get a cough / runny nose etc - but not full on croup - Its as contagious as a cold - I keep my son away from pretty much everyone when he has croup - but its really the parents decision I guess - Boys are more prone as their windpipes are smaller & should grow out of it by the age of 7 - when my son is over the worst of it I always tell parents that may wish to come over etc that he has had croup & then its their call - Its a terrible virus though - I wouldn't wish it on anyone - Not so bad once U know what U are dealing with though