To ease my worried early pregnancy mind, I borrowed a pocket doppler from a friend. This would let me listen to the heartbeat whenever I wanted to - which, before I started getting consistent punches to ribs, was a LOT.
A few times, I asked Christopher: "Chris, do you want to listen to the Baby's heart?"
Because of that question, Christopher started calling the baby "Baby Heart." The name has just stuck, and that is what we call her too (if we don't hurry up and decide on a name in the next few weeks, I guess she'll just be Baby Heart for forever).
The other day, Christopher was running around the backyard. I was sitting, watching him run back and forth. He stopped, ran up to me, looked at my tummy, put his mouth to my belly button and said:
"Hi Baby Heart. What are you doing? You swimming in Baby Heart's room? I Christopher!" And then he zipped away.