There are just a few authors that my 12 year old and I trust implicitly.
After having raced through umpteen of her novels, we may have placed Diana Wynne Jones in that category. Sure, The Magicians of Caprona was kind of stupid.... But if you locked us in a library, with a short deadline in which to emerge with a book we were willing to read, it might very well be one by Diana Wynne Jones.
Cart and Cwidder is a light-weight but enjoyable and typical Diana Wynne Jones offering. There is the standard DWJ mother -- self-involved and mostly oblivious to even the most obvious danger to her children. There are the children whose future depends on their learning to take advantage of their gifts, innate and physical. In this case, the gifts are their ability to entertain, spin tales, and play the musical instruments left to them by their murdered father.