I'm having the same problem as outlined in How can I get my cat to stop nursing from its mother? My kitten is about 12 weeks old, and is still nursing. The mom tried pushing it away, but the kitten would just beat on her and pounce her until she gave in. Now, she doesn't fight at all. She doesn't seem to mind now. However, the nipple he is feeding on is huge. I mean 3 times the size they were after she had the kittens and was nursing. (She only had 2 and 1 died) The nipple is so big and heavy, that it hangs down a lot. There is also a red line around it ( the fleshy area is huge around the actual nipple) and bite marks around the actual nipple where it feeds.
The kitten is eating hard food. There are 3 food dishes always full around the house. The cats also get some people's food as treats, and milk from cereal. Little bits. It's certainly not lacking food.
I don't know what to do about it. It does seem to be hurting the mom. She was barely an adult and a stray when she became pregnant. My male knocked her up and brought her home. He's been an active father.