Yes, I plead guilty. Before I wrote literary fiction, I wrote formula series. And this is the granddaddy (grandmommy) of them all: Sweet Valley, became an international bestseller and even a TV show. I was only one of its stable of writers, working under the pen name, Jamie Suzanne. But the books I authored for the series helped me put my children through college and, in fact, supplied the "switch and bait" that led many youngsters to far better books –thank goodness!
As Buddha said, "This, too, shall pass," and Sweet Valley is no more. But you may be able to find some collectors' and used editions here.