Incidentally, despite the title of this pic, it's very unlikely for that woman to be that kid's mom.

I also doubt that they are a couple. Brother and sister is what I'd go with.

It's impossible for them to be siblings too. Otherwise that kid would have blue hair like her's. I tagged it couple since I didn't know what else to call them in this picture.

Um... you guys do know people can be related without having the same hair color, right? Maybe the kid's father is blond. Shocking, I know.

It has more to do with the context of the story, I mean.