Disclaimer: I can't understand why any white couple would want to take a chance on adopting black children from anywhere -- it makes no sense to me (from a point of "reasoned racial reality").
My sister and her husband went through a well-respected Christian adoption agency for their two adoptions. After the first adoption of a little white baby girl, they learned of an available child whose biological mother wanted them to have her daughter. She had seen their profile and thought they'd be suitable.
They had no idea that the child was biracial. The mother was an older white woman who, apparently, had a drunken one-night stand with a black guy whose whereabouts are now unknown, and voila! guess what happened! In any event, she didn't believe she would be able to raise the child.
When my sister learned the newborn was biracial, she was worried that she'd be able to love and raise the child. It was a bit of a surprise and the agency, I believe, failed to mention it. Nevertheless, the baby arrived and they loved her and raised her. She and my sister have developed an incredibly close relationship.
My niece is now in college. She's a bit conflicted over her ethnicity. Yes, two white people raised her and gave her everything she ever needed. Yes, her sperm donor was an anonymous loser. But she still seems to see herself as black and believes she should identify as such. She's 20 now, and I'm hoping she'll come to an understanding that the hue of her skin is of minimal importance.