The anatomy of wish fulfillment is this latest Cinda Hollister story of Janet Lambert's. Take one happy, well-provided-for New Jersey family, set them up in a modest little mansion, add a long, glorious summer and pepper with scores of bright eyed youngsters of conveniently matched ages. The result -- golden days, clouded, perhaps by a minor clash between the town's rich boy and a pretty Southern girl, or the gentle sufferings of the little polio victim Thelma. But the clouds soon pass, thanks to elf-like Cindy, who is just incidentally wholesome, sensible, and talented, an average American wonderchild. Janet Lambert, whose books are favorites with girls, writes with a spirit and conviction that will probably win the Big Deal many satisfied readers, but even her professional facility cannot fill in the gaps in depth and substance which riddle this book.