This is one of our current fosters.
He is half the size of the litter he came with and we still syringe feed him supplemental formula to keep him gaining.
Here is a photo of him next to one of his supposed litter mates. We think someone just threw a cat from another liter with the other kittens when they got sent up from Tennessee.
His name is Sebastian, but since he is half the size of his litter mates, (and in honor of parks and rec) we call him Lil Sebastian he was 250 grams versus 556 grams the orange tabby next to him weighed.
A food scale to weigh kittens is good way to make sure that the kittens are continually gaining weight. (A sign they are doing well) we weigh them at least daily since they can't tell us how they are doing. It gives us a good guide on how healthy they are in general. They should be gaining weight every day...