Of 3,200 children’s books published in 2013, just 93 were about black people, according to a study by the Cooperative Children’s Book Center at the University of Wisconsin.
There's a lot in this op-ed in the NYT that I want to quote, so you should probably go read it if you care at all about children's lit. Also check out the raw data from the study, as the Cooperative Children's Book Center documents much more than this single metric.
"We adults -- parents, authors, illustrators and publishers -- give [children] in each book a supposedly boundless imagination that can delineate the most ornate geographies, and yet too often today's books remain blind to the everyday reality of thousands of children. Children of color remain outside the boundaries of imagination. The cartography we create with this literature is flawed."