I'm an average human. I suck at empathizing outside my circles of association, and I wish for Save the Children to know that this ad is effective.
Because the girl is white? Not really. Because she's English? Well, maybe. Even though I'm American, English culture is not that different from my own, so I can't tell myself that the girl is from some Uncanny Valley where people either somehow enjoy going to war, or are doomed to keep having wars because of their hopelessly broken culture. It might even help that she's English rather than American, because the video makes me think of World War II, in which this kind of thing really happened to English civilians.
And lastly, it focuses on one person. They're not asking me to help end war, which is a goal that promises soul-crushing defeat, but to help the person this girl represents, which is achievable, and worth the effort.