It's normal, if they are males... that's called the "cere", and is a helpful characteristic to look for/at when determining their sex when they have abnormal/incorrect or asymmetrical wattles. Only the males will develop this fleshy lump.
But if they are females it could be some sort of infection, or wound causing some swelling. Usually with swelling tho there is some type of discharge or they have gunked up/plugged nostrils and you can hear they have problems breathing.
Watch their behavior, if they shake their head a lot, or sneeze frequently then I'd catch one and check them out up close. My guess is that it's just the males in your flock are fully maturing tho.
I have a few males that have very prominent ceres. I'll try to get some profile pics of them tomorrow.