It came from the mouth of a 6 year old girl that I met on my flight to France. Now, many might tend to do this away as one of those strange things kids ask. But I think there is more to it.
As I understood later, this question was purposeful; because after asking this the little girl continued by asking the little boy she was talking to whether he had the same eyes as his father.
Could it be that kids nowadays are very concious of the fact that someone might NOT have a father because they might have two mothers, or a single mum instead?
I don't know the answer but I find it utterly intriguing!