Talking about Adoption with a Toddler

I read somewhere that kids can't truly understand the concept of adoption until they are about 5 or 6 years old, and that every conversation you have with a child before that age is really just practice for the real thing. I think the hardest thing for me about talking to Evie about adoption is finding words that are at her comprehension level to express such big, important and somewhat abstract ideas. She's still a little fuzzy about the terms "boy" and "girl," so the concept of "first parents" and "adopted" are way beyond her ken.

Tonight we read the book I Wished For You at Evie's bedtime, and afterward had a conversation:

Me: "Evie, you know you were adopted just like Barley!"

Evie: "Adopted."

Me: "Yes, we adopted you. You know that R and G are coming to visit us tomorrow; they are your first parents."

Evie: "First parents."

Me: "Yes, when you were born you came out of R's tummy and then Mommy and Daddy adopted you."

Evie: "And we eat cake!"

Well, at least she has positive associations with adoption at this point? :)