well first go to emergency threads, that'd be a better place to look for advice. I had a problem kind of like this but it was one full grown chicken so idk. Start a thread in the emergencies/diseases/injuries/cures forum- you can get help there
This happened to one of my hens 4 years ago. We could't find any signs of bruising or breaking, so we just nursed her by feeding her plain Greek yogurt with crushed layer pellets mixed in, and helped her drink by holding a cup for her or using a dropper. we also made her go for short walks...