My dad once said to me, "You give a lot of books three stars." I do.
Seems similar to the Magic Tree House books. I've only read one, but I'd guess the series is the kids returning to Droon over and over helping solve problems in the land (though maybe there's occasional crossover from Droon into this world?). Nothing really stood out to me as being really interesting or original in this first book, but the eight-year-old likes them.