I can't remember if I've said this before:
Nick and I were playing with cars a while back: I was the mommy-car and Nick was the kid-car. I kept calling Nick "little-one" and he came back with "mommy-one."
I just started calling Nick a sweetie-pie lately, mostly because he is! He was picking up some toys and I asked him if he needed help: "a-course, Mommy-pie. Fanks!"