I have two 7 week old kittens. I've had them living with me for one week. My friend owns the mother and said that once the kittens started eating real food that I could take them. I've just started noticing about two days ago that one of the kittens is sucking on the other kitten. When I pull her away, she goes right back and continues sucking on the other one. What should I do? Take her back to her mother? Should I keep pulling them apart whenever she does it? Please help.