CBS News Correspondent Susan McGinnis found out for The Early Show. She went to Somerset, Mass., to meet a single mom and the anonymous donor her two kids now call "Dad."
"They knew that they didn't have a dad in their family and that was OK with them," Raechel McGhee says about her children.
Until recently, Aaron and Leah McGhee had never met their father and, what's more, neither had their mother.
"If anybody said, 'Where is your daddy?' They would just look at the person and say: 'We don't have a daddy in our family," Raechel McGhee says. "We have a donor.'"
McGhee used a sperm donor to have her children, and signed an agreement that the children couldn't meet the donor until they turned 18. But when McGhee learned about a Web site created to bring siblings of donors together, she took a chance and posted a note with her donor's number.
"I just put, 'Donor if you're out there, thank you. These are the most beautiful children in the world. They're the greatest gift. We wish you everything good. Thank you, thank you, thank you.' "
McGhee's sperm donor, Mike Rubino, immediately wrote back.
"As soon as I read the message," he says, "I hoped that, and I felt that, it was likely that I would be in some way a part of their lives."
"And there it was," McGhee says. "And I said, 'Oh, my God, this is him.' "
Rubino says McGhee phoned him and they talked for a long time. "That brought it home that I have kids," he says. "They have names. They have ages. They became absolutely real at that point."
"It was emotional," McGhee says. "It was surreal. It was beyond description for both of us."