I have 271 book recommendation posts on my blog--some of those include multiple books. When I started the blog ten years ago, there wasn't such a big push for diversity as there is now. Recently, I was curious how many of my entries were about diverse books. Doing some research, I discovered 49 of the entries had books with diverse characters who were integral to the story. (That's about 18 percent.) The books were not necessarily fully focused on diversity, but at least presented an important character who was nonwhite or other "abled." (If you want to see what books are included, search my blog for diversity or go to this link where I've done the search for you.) If I'd looked at the fantasy books, many of them would fit the diversity category too, as fantasy books often deal with characters who are different from the mainstream of their culture, but I don't think those books are usually counted as diverse.
I didn't set out to read "diverse" books specifically. Fortunately, I was raised to believe people are people despite skin color, cultural differences, etc., which means when I hear of a good book, or pick up a book, I'm not automatically offended because the main character is not like me on the outside. What I see as I read is that these characters are so like me on the inside. Which is why it is so important for "white" kids, "abled" kids, poor, middle class, and rich kids to read these books. They need to see we are more alike than we are different!
On the other hand, according to the 2015 Census, about 62% of Americans are white only, 17% are Hispanic or Latino only, 13% are black only, 6% are Asian only, 1% are Native American or Alaskan, and 2.5% are two or more races. (Note: Arabs are classified as "white" for censuses.) And these statistics don't include "differently abled." But even with these skewed figures, it'd be hoped that good books are written by/about 40% nonwhite "abled" people. Because people who fit these "other" categories deserve to see themselves represented in story too.
The reality is we're not there yet. Look closely at the above infographic. You might find this source post from September 2016 of interest. And here's an interesting post on CCBC on how books are counted.
What can I as a white writer do? Deliberately support those writers who write diverse books by blogging about those books, buying them, sharing about them, etc. And support diversity organizations. I just came across this list: 2016 LINKY (Diversity Children's Books Reviews). It can be a source for me to find books. Plus, I can let people know about it through twitter, etc. And, of course there's the We Need Diverse Books organization. This site has links to awards for specific types of diverse books. Again, it's another source to find books that I can share. SCBWI has a page on their site that focuses on diversity, plus has two diversity grants. Several of these diversity sites want you to notify them if you know of books, awards, etc. not on their lists. That's something any of us can do.
FYI, Multicultural Children's Book Day is coming up on January 27th. You can download a free kindness kit here.