My wife is the daughter of Filipino immigrants, so obviously my kids are mixed race and we don't fit the profile of a "white" family, but my take from your comment is that you spend way too much time thinking about tribal identity politics.
If I'm writing a short story (let's say it's fan fiction for "Little Women") about a family in a New England village in the 1860s, images that include non-white people in them are going to look absurd and be ahistorical. Your assumption that the only reason to prompt for an image of an ethnically homogenous family is due to bigotry appears to reflect a negative and pessimistic view of humans. I would guess this view stems from spending too much time reading Twitter comments and forgetting that they are written by a tiny, non-represenative sample of the population that skews towards derangment.