You have never read a little golden book[0]? The back cover is often ads for other kids books. I recall the Goosebumps books did the same with a PO box that you

You have never read a little golden book[0]? The back cover is often ads for other kids books. I recall the Goosebumps books did the same with a PO box that you could send a check to in order to get more books. Sci-fi paperbacks often have ads for other books as well. [0]https://en.wikipedia.org/wiki/Little_Golden_Books https://en.wikipedia.org/wiki/Little_Golden_Books