I really like this book, put out by Scholastic, as part of their First-Start Biography series. I've looked for years for a good Squanto book, not too hard, but not too babyish, that still has good information. We really don't know that much about Squanto, but I like this book as it seems like it has the most accurate information (Squanto scholars out there, correct me if I'm wrong, but in a nice way, please).
Summary and image from Amazon:
A simple biography of the Wampanoag Indian who helped the Pilgrims survive in their early days in the Plymouth colony.