Faith, on the Hoping to Adopt Blog, recently asked the question,
"What does your child call his birthmother?". Certainly not the first time the topic has come up on the blogs, it always gets people talking.

I still chuckle when I recall
Coley writing about her son calling her his "burp mom" ... and getting downright possessive about her, too, if I remember correctly. ("She's MY burp mom!")
Seriously, however, this is a tough issue for those of us without the option of open adoptions. Conveying the importance and depth of relationship to someone never seen is not easy with young children.
A kid can understand a burp. Birth, on the other hand, is completely beyond their gasp. It's up there with death on the list of stuff a little kid just can't, and shouldn't, comprehend too fully for a while.
This is NOTHING like the same thing, but will serve as an example of how young children interpret the aspect of the world around them, especially those that are less concrete than daily, touchable experiences.
A while back a friend of ours
lost his 11-year-old son to leukemia. This tragedy just happened to coincide with the death of two of Sam's rabbits.
Mark, being a pragmatic former farm kid, brooks little sentiment over the likes of rabbits, so dispensed with the remains posthaste and explained the process in only basic terms.
On our way to Rannick's funeral, Sam asked, in that oh-so-genuine way that four-year-olds have of asking when an answer is really important to them, if they were going to throw the dead boy away like Dad did the rabbits. (That got Mark understanding the useful lesson potential of pet funerals, maudlin machinations and all.)
Sam is anything but a cruel child, and has a great deal of compassion and a very caring nature, so his query had nothing to do with gruesome speculation or any morbid fixation on disrespecting remains. He simply needed to know what would happen to what was left of Rannick. I have no doubt that, being four and already aware of some of the dangers of life and familiar with death in the abstract, whatever answer he received would tell him a lot about what could happen to him, as well.
He didn't get the idea of the coffin, and references to burial made no sense to him at all, since we were in a church at the time. I ended up having to leave the funeral service early because he decided it was a great opportunity to tease his sister and have other such uproarious fun, so it was obvious the gravity of the occasion pretty much escaped him.
He's mentioned it since, always in connection with dead rabbits, though, so that link will be there for a while.
He's recently been wondering about where the other kids in school were born, and was a bit surprised to learn that none are from Cambodia. (In his experience, that's where babies come from, after all.) How they came to be has not entered the realm of questions yet.
Broaching the subject of birth parents has been done, but so far he has no interest in examining the topic. Unlike Grandma Janet who sends him boxes of goodies from America every month, those who made him have yet to appear on his radar.
We have no names for these people, no photos, nothing at all for him to attach a thread to, so building a reverence in him will be a long process. Loving himself, being proud of his roots, understanding his birth country and culture, valuing diversity, learning his story, and building upon the relationships we do have will, hopefully, all serve to help him to forge a connection to his beginnings, and to the man and the woman who were there and made him happen.