When my "middle child" kitty (the black-and-white one) was a baby almost 10 years ago, he used to suckle on my stuffed bear. He would knead his paws on the bear's belly, and simultaneously suck on an arm or an ear. I figured that he must have been separated from his mother too soon, and he found it comforting.
Oddly enough, it wasn't as if he suckled on everything like this. Just the one stuffed bear. Somehow my teddy bear had become a replacement mother for him, or something.
He did it for years, even way past his kittenhood; I think it just became a habit. When the youngest kitty (the tortoise-shell) came along, she saw him doing it. Being a baby herself, she imitated him. But she didn't suckle, she just kneaded on the same bear's belly -- and she always had a bit of a puzzled expression on her face. Like, "I don't know why we're supposed to do this, but I guess we are...."
They both still do it now and then, but not very often anymore.