Okay. Take the baby from mom (gently, with his intestines), wrap him up, and put a dab of honey on the gums. Attempt to gently put one drop of KMR at a time in its mouth. Kitten must be tummy down, head up. Prepare the milk and honey before taking him. Is mom even snuggling him?
Ok, does not sound as though he's tried nursing yet. Let me know if he tries to nurse. If not, try to help him as I described above. If he makes it to morning, take him to the vet. They may be able to repair him. If not, they will euthanize. He should not just suffer though. Human babies with outside intestines are repaired and live.
You will need to try to supplement. He'll die otherwise for sure. She won't like you taking him, but do it in front of her. Otherwise, he'll just fade out with mom.