I think this happens more than you would think. I had a cocker cross that would get in the box with a calico's kittens to take care of them. It was a very cold winter and I knew it was just too cold outside, so we brought them all in the house. When it was time for the Momma Calico to nurse, I would have to pick Mitsy up and put her in another room. She thought those kittens should be hers.