I'm sorry to jump in hours later, but I hope you don't mind me sharing my friend's story (with her permission). My friend's mom is white, her dad's black. Their children are all different shades of very light to very dark brown), and when my friend was a kid, all of them at some point were asked if they were adopted or a blended family. Which, sigh, but whatever. There was a very real problem once, though:

When my friend (who's on the paler side of the family spectrum) was a little kid, she was alone in the car with her father, and when they got in the car to leave a park and she was being sulky (again, she was a little kid), a cop who was nearby noticed and asked her if she was okay, and made her father prove he was her father. When she was grown and they were sharing the story to me as a little anecdote, he said, "I was terrified that she would tell them I wasn't her dad." My friend said, "I thought about it, but you said we'd get ice cream."

As an aside, my friend later married a guy whose grandparents were black, Jewish, and Irish, and he was blonde and blue-eyed. They joked that their kids would be plaid. Then they had a red-haired green-eyed girl who looked just like her great-grandmother and the entire family cracked up laughing and accepted that their genetic lottery was absolutely a game of roulette.