Tyson and I had this conversation the other day when I went to get him out of bed in the morning.
Me: "Good Morning Tyson!"
Tyson: "I wake up Mommy, I wake up!"
Me: "You DID wake up, did you have a good sleep?"
Tyson: "Yep. Baby sister wake up too?"
Me: "Yes, baby sister woke up when Mommy woke up."
Tyson: "I play baby sister?"
Me: "Not yet, she's not ready yet."
Tyson: "Baby sister come out Mommy's tummy?"
Me: "Yes when she comes out of Mommy's tummy you can play with her. But we have to wait a little while ok?"
Tyson: "Ok Mommy."
Since then another conversation very similar to this one has happened. I think he understands what's going on... we've always kinda wondered what he really thought was happening.