If that the tuxie the mom is ignoring? Do you feed him with a dropper or syringe?
Winter, they all white kitten, is the baby that the mother won’t feed. I have a little syringe with what they call a miracle nipple on it. The kittens really like it and are able to latch onto it. Of course she’d rather have mother’s milk and will rarely take the formula. I just have to get her to about 5 weeks old, three more weeks, and then she can eat what food all she wants.
The poor little tuxedo is about 7 weeks old. Different litter, and some ex-friends saddled me with him. Of course I’ll take care of the kitten, I’ll never put him back where he was, but they didn’t even discuss it or take any responsibility. But it actually works out okay, I never liked them and just had to be polite. Now I don’t have to do that even anymore.