I work with children and none of them to my knowledge got the idea that all white people are bad from this book. I find it odd people think this is inappropriate for children 6-10 years old even though we teach them other history. I mean I wonder how you schools are celebrating MLK Day if they aren't mentioning racism to elementary aged children.
Furthermore, we act as if 6-10 year old kids did not experience this. This book is based on a real court case involving Sylvia Mendez. Just like Ruby Bridges (a child) or other students of the time, they were not segregated from the school by just a few bad people but by laws made by people who thought they were racial superior. Those people used racist slurs against children and that is historical. I've had kids younger than 6 be able to handle challenging topics like this with appropriate discussion and give interesting insights. Kids this age absolutely recognize race and other differences and that is OK what is not okay pretending like people don't get treated badly for those differences.
The drawings are part inspired by Mayan art and the characters in the book are styled in 1940s children's clothing. Not sure why another review found that the characters looked modern.