I did some research on the internet and I came across this. Does this sound like what your baby does? I also looked up Merk's disease, but it doesn't sound like that to me. It sounds like this. I have two polish with the big hairdos , I keep them away from the other chickens in a coop in our garage. Let me know if you think this may be it.
Blessings to you and your chicks...
Water on the brain
The best silkies are those with a dome on their skull which produces an excellent crest although this is often quite alarming when seen in chicks as it appears as a large bump on top of the head – quite disconcerting to new breeders!
It is a particular problem with, although not limited to, some of the crested breeds and is often mistaken for Marek’s disease. An infection in the enlarged cranial cavity produces fluid which in turn presses on the brain. Symptoms include walking backwards and falling over. The bird may spin around in circles then suddenly recover, much to the misguided amusement of the keeper.
Treatment is simple and effective: isolate the bird and administer a liquid feed (pellets ground up with water) via a large syringe directly into the mouth at regular (two to four hour) intervals during the day, with the last feed at night.
An antibiotic preparation needs to be prescribed by your vet and injected into the breast muscle along with an anti inflammatory drug (ask your vet to show you how if you are unsure) to reduce the swelling and clear up the infection.
You may have to continue treatment for up to four weeks in mild cases however severe cases should be euthanized if there is no marked improvement after one week or if the bird is in considerable distress.