Almost every children's book that depicts a serious issue, such as racism, tells a complete story where the problem is solved and is no longer a problem. I believe this is a big part of why so many people think that racism (again, for example) isn't a problem anymore.

Because, they learned, from a very young age, and for many years, that such problems were solved.

There is a very strong and understandable impulse for children's books to be comforting, and to shy away from un-answered questions. This, as you point out, leads to a warped view of reality that parents then should correct.