Baby with naked bum

[StaleCookies]

Two of my chicks have naked bums but one is a lot worse than the other. There is a little redness around the bald patch on the worse one and the bald patch is pretty big. I don't know how old they are but would estimate 4 weeks. Is there anything I can do to help?

 

[Cheekychook12]

Two of my chicks have naked bums but one is a lot worse than the other. There is a little redness around the bald patch on the worse one and the bald patch is pretty big. I don't know how old they are but would estimate 4 weeks. Is there anything I can do to help?

Pictures would help, having some bald spots is normal for pinning chicks, but redness may indicate a problem