Our girl (1 yr old) just recently had 4 kittens 3 weeks ago. While they all seem active, curious and vocal, I do have concerns for one of them. While the other 3 seem to be filling out and wandering around and playing, 1 tends to sleep in a corner alone, and isn't generally too playful. He also is more slender in build, with his hips bones and spine poking out MUCH more than his siblings. My wife and I have done some research into his symptoms, and stumbled across "Fading Kitten Syndrome", and while most of his signs fit, I'm not 100% convinced. While he is much skinnier, he is eating quite regularly and doesn't have a problem with feeding. He's also responsive to our presence, and perks up and moves quickly when the mother enters. He's also quite vocal, probably the most vocal of all 4. All of these symptoms don't seem to fit the "fading kitten syndrome" bill, except for the "lethargic" behaviour. I'm reaching out to anyone that can shed some light on if this is normal or not, and whether or not I should be worried. It's been a while since I've had to take care of kittens. Any help would be much appreciated! I can also take pictures if needed.