NP, we actually don't call them christenings. That is more of a Protestant term used for Baby Dedications, which are also a beautiful ceremony. Baptism is seen differently among different Christians, as you probably know.
OP, I don't see why they wouldn't be able to come up. When we adopted our first child we told the priest that our DD's birth mom would be at the Baptism and we wanted to honor her in some way. He spontaneously invited her up to the altar with us during the ceremony, and did a prayer "blessing of the mothers" that he made up on the spot. She was really touched.
at 12:03 AM on Apr. 21, 2011