A while back we were babysitting the two daughters of some friends at our house. As the older girl--a kindergartener--and I were exiting the playroom, she suddenly said, "[Puppy] didn't grow inside of you. He grew inside of another woman, and she couldn't take care of him so she gave him to you to take care of."
"That's right," I said, a little surprised. "The woman's name is K___. That's a picture of her over there."
We've never talked adoption with any of our friend's kids, although we certainly have with their parents. Her mom is pregnant with their third child, so siblings and pregnancy have been a big topic of conversation lately in their house. My guess is that the little girl had been asking about our family and her mom had tried to explain why I hadn't been pregnant.
Earlier that same evening we had been playing with our two house rabbits and she had asked if the bunnies were girls. Upon hearing they were, she immediately wanted to know whether they could have babies.
"No," I replied. "They had an operation, so they can't have babies anymore."
"My dog had an operation, too. She can't have babies either," she told me. After a pause, she asked, "What does the operation do?"
"They take out their uterus. Without a uterus, animals can't have babies."
That answer seemed to satisfy her, and she turned to leave the room. Halfway across she turned back to me with a smile.
"My mom sure has a uterus!"