nervous

I had a little girl 6 years ago, and put her up for adoption. We have an open adoption, her parents divorced a couple years ago and she and her mother now live in the same town as I do. I have a child at home now that is 4 and one on the way, it looks like the girls will be attending the same catholic school next year, does anyone else have this kind of situation? Both girls know about the adoption (in young children terms). They call eachother sister, they get along very well. Do you think this will be awkward for them as they get older? I feel like now we are spending some of the holidays together and we are getting so close that its almost as if we are meshing into a somewhat unconventional family, I like the feeling, and I dont want this dynamic to change.