The new mom usually chews through the umbilical cord on her own, but if she doesn't then you will need to step in and cut it.
Kitten Umbilical Cord Bleeding
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This is especially likely to happen if the cord comes off early due to being accidently tugged or pulled. This bleeding can occur right after the cord falls off or can happen as much as a week later. The mother also chews off the umbilical cord.
It looked like at good amount of blood for his tiny body, but it seems to have stopped.
Both the kittens still have their umbilical cord connected to them, and the momma cat won't cut it off, or go near it. This should stop the bleeding. As the kitten is born, the umbilical blood vessel is pulled, eventually snapping off, which in turn pulls the abdominal wall. It looked like at good amount of blood for his tiny body, but it seems to have stopped.