My wife and sister in law are both adopted, as my in-laws couldn't have kids for one reason or another.
They have never known anything different, never had the facts hidden from them, and are a very tight knit, intact family without any unusual issues.
They have one set of parents are are both extremely grateful for the gift that their parents gave them.
After all they were "chosen...," my wife in fact by her older sister
So...with that said,
Congrats to you and your growing family.
You have given some lucky child a special gift. I encourage you to pass your generosity on, as I am a firm believer that "nurture" trumps "nature" supremely.
-bear