Yes, they do. If you want to protect the chicks, you can try mixing powdered sugar and plaster of paris
in a container, and leaving it for the rats, preferably not where the chooks can get into it. The rats will eat it and yes, it is eventually fatal if they eat enough of it. I don't like to do that to any animal, even a rat, but it is better than having rat poison around and sometimes you have no choice. And it does work pretty well. WE have had rats in the past eat eggs with embryos right out from underneath a setting hen at night. Now we have two barn cats who stay in the barn all night and it does seem to help to have them there. I don't know what to do about your chick's leg, if you're sure it's broken and there's no way to splint it. Someone may have an idea to help you. Can you bring the chicks inside til they get a bit bigger?