Something wrong with chicks. Pls help!

[Claire85]

Hi
I had 8 chicks hatched out on 18th June, and on Sat I went down to find one in the house dead. He had a large swelling, like a bubble on his right shoulder. I assumed he had got hurt in some way. But now this morning the rest appear to be getting the same swelling, all in the exact same place!
Any ideas what this could be or what to do? I've never seen anything like this and can't seem to find anything online. Please help

 

[Sylvestor12]

I'm not sure that the bubble means something because I have a Polish hen that had an air bubble on her shoulder and it never bothered her. Now, it's gone but it didn't affect her as a chick.

 

[Claire85]

I'm hoping these will go away as well. Have been checking on them and they all seem to be ok and the bubbles aren't getting any bigger thank goodness. Would love to know what it is though, have never seen it before!