Here is the summary from Goodreads:
Luckily, his daughter, Sarah Claus, knows who to call for help. The Lambchop family! But can they convince Santa that there are still good children in the world? Just leave it up to Stanley.
Once upon a time, Stanley writes a letter to Santa that really touched the big guy's heart. But when he lost his Christmas Spirit, Santa's daughter decides that the one thing that will bring it back is a visit from the Lambchop family. Stanley, and the rest of the family, show Santa that not all people are angry and selfish, that not all hope has been lost.
I think this is a holiday book that your blossoming readers will enjoy (those who are ready for chapter books, be it in second grade or fifth). It is a quick read, with short chapters and some pictures.
Seasons Readings page to check out the other books/reviews and to link up your own!