Because a white male is in no way "ethnic".
Exactly.
Per
http://en.wikipedia.org/wiki/White_people you can clearly see that "white race" or "white ethnicity" is a misnomer. Many ethnic groups are characterized as having white pigmentation in their skin, and there is no single ethnic group that comprises the whole of those people that are "white".
It's perhaps a little less true with black, but it depends on the country. In the US black people can primarily trace their heritage and ancestry to a very few African locations. Go to Europe, though, and you'll find many more separate ethnic groups that all share dark pigmentation. The US is following suit as a lot of African people are immigrating. I used to work with someone from Nigeria, and he did not identify with the existing black population in the metro detroit area simply because he shared the same skin color.
So while you may feel indignation at being marginalized by a children's show, I don't think it's a valid complaint. In other words you're also being marginalized by me. How does it feel, living in the margin like that, huh? huh? Yeah, not so good does it? Wait, where was I going with this? Nevermind. Have a picture. Pay attention to the shape of the head, eyes, and noses.
And despair.
Added at: 08:42
I wonder if overweight is an ethnic group, 'cause that boy in the front middle has some junk in his trunk, and it's no wonder he wears suspenders. I think all obese people who wear suspenders should picket the publishing company.