I have a moma cat who had kittens about eight months ago. She had three and we kept them all. Moma cat recently had another litter but sadly these babies didn't make it. She rejected them. In the last 2 weeks moma cat has started nursing the older kittens that were born about 8 months ago. Is this normal or will this hurt the moma cat? The kittens are as big as moma is and so it looks funny when we find them nursing.

A lot of animals will adopt babies that aren't theirs when they lose a litter, so I wouldn't worry too much about that part. What I would worry a little bit about is three full grown cats nursing from her, because her body just isn't built to produce that much milk. If they're nursing too much or too often, she might end up losing weight and getting sick from malnourishment. Her body will automatically put whatever nutrients are needed into making milk, not leaving enough for herself.

If the behavior doesn't stop on its own, in a couple weeks and before she starts losing weight, then you'll need to wean them. When you see them nursing, chastise them and pull them away. If that doesn't work, then you can take a sock or shirt sleeve, depending on her size, and cut it so it's a tube and slip it over her abdomen like a tube top. That will make it hard for them to nurse, but she might take it off and you'll need to readjust it several times a day. A last resort would be segregating her away from the rest of the cats until her milk dries up, probably at least a couple weeks. However, I would be hesitant to do that since she just lost a litter and obviously needs contact with the other cats.

I would avoid typical aversion therapy methods, like spraying water or making a loud noise when an unwanted action occurs, because it would also punish the mother and it might discourage all of them from being around each other. I doubt you want a house of cats that are afraid or unwilling to be near each other.

You could try putting cones on the kids, but they would have to stay on for at least a couple weeks for mom's milk to dry up, and a lot of cats don't handle cones well.

Have you thought about getting mom fixed? Are the kids fixed? It would prevent any future trauma from losing another litter, and keep you from ending up with 27 cats in your house.