"Mommy, I really hope I can get a baby brother or sister one day."
"Me too baby, me too!"
"M-O-M, you already have a brother AND a sister!"
"No, I meant I really hope you get a baby brother or sister one day"
"We're trying really hard to make that happen. That's why Mommy has been going to the doctor and taking those medication. It's hard for Mommy to get pregnant. That's why you are such a special blessing."
"Oh, that's why you had to go to the hospital and have your blood taken?"
"Mommy, I hope when I was a baby I didn't drink all of your milk up and that's why you can't have another baby"
(While holding back tears) "No sweetheart. When a Mommy has a baby their bodies start making milk right then for that baby. A baby can't drink up ALL the milk."
"OK, that's good!"