Adoptive Mom

I have been reading a lot of blogs written by adoptive parents. I follow a woman who is single parenting two boys in the States. I was reading a blog post by her where she was explaining why she had canceled a visit to the first/birth mom..... in it, she mentioned something about being an adoptive mom....and a mom. It got me thinking....and I get what she was saying. I always felt like Adrien's adoptive mom, like there was someone out there who was his "real" mom, and it wasn't me.....like a long term nannying gig..... about a year ago, probably due to tons of reading, huge bonds and time, I finally felt like his mom.....that me, just his mom....and I love it.....though I clearly remembering feeling like his adoptive mom for a long time....and I can't explain why.....

My neighbour is pregnant and I am taking the opportunity to engage Adrien in some conversations around adoption..... this was our conversation the other day:

Me : What does neighbour have in her tummy?

Him: A baby....mommy, you have a baby in your tummy?

Me: Nope, my tummy can't have babies in it.

Him: I come from your tummy

Me: You have another mommy.....you grew in her tummy.

Him: where is she?

Me: I don't know (I really don't, due to circumstances, ours is a closed adoption)

Him: We go to Wal-Mart and get me a sister?.....and he was off.

I am trying so hard to be correct with the terms I use with him and what I tell him...... It's hard, cause I don't want to mess it up for him....I never want him to feel ashamed of being adopted and I want him to know that he is loved by many people, including his first family, even though they don't see him......suggestions? input?