I ordered some cochins in the spring. Even with them all being the same breed, they all kind of grew at different rates. I had some sprouting feathers all over and others that were still covered in baby fuzz. Eventually everyone caught up though, and now they're all the same size. I do have one that is blind in one eye, and she was having trouble gaining weight. A little TLC and some gamebird feed fixed her right up though. Good luck, I don't think your birdie is a bantam- just a slow grower.