I think it's because their skull isn't closed all that is under that fluff on top of their heads is a bit of fatty skin.
Do you have a way for them to get into the pool steps or ramp?
Are you giving the little ones so supportive care like vitamins? You lil crested may benefit from some extra nutrients
what makes you think your crested is a drake ?
I know about the crest, i asked how common it is for them to have problems ???
Yeah i have a good size rock so they can step into their pool.
No vitamins but i can get some, what do you recommend?
I think it's a drake from the way it acts. he doesn't make much noise at all (and the non crested khaki and the Pekin are getting their quack, I've heard no quack from him, but I know it could still be female and just quack late) and he's super docile and sweet. Also, he's the only one that will chase off chickens.