A Lonely Desperado!

I think you need to consider coccidiosis as the cause - they are at the prime age for having been exposed to and overloaded by cocci - and your description of the symptoms sure seems to fit. When in doubt, treat first - question later on coccidiosis. This is not about the watermelon and yogurt/vinegar is not going to fix it.

 

Are you in the US? If so, go to Tractor Supply and get some Corid powder or liquid and treat them for coccidiosis. If you are in the US, what state are you in?

-Kathy

 

Are their wings drooping and hanging down along their sides? Are they huddling at a heat source all the time? Those are two other signs of coccidiosis. Coccidiosis kills young chicks very quickly; chicks can go from normal to dead in less than four days. If their wings are drooping and they are lethargic under heat lamps, you don't have much time left to treat; they need meds or they may be dead in a day, two at the most. What is the time frame of what you're experiencing?
There could also be bacterial overload, such as e. coli. The best bet may be to put them on a broad spectrum antibiotic as well as a med for cocci. The weaker the chick the more likely you'll have to hand feed it medicated food or water.

 

It will not help them!

-Kathy