Why does my female cat chirp and coo at the new 6mo old female kitten in the house ?

I'm catsitting a friend's cat. My older cat is very happy to see the new cat and wants to play with her. the new kitten is scared and hides a lot and doesn't want to come out to play. My cat was making chirping and cooing sounds all last night in the room with the new kitty. Has anyone else experienced this?