From Amazon:

In a series of letters, a young girl writes to Santa to ask about the North Pole, Mrs. Claus, and of course, Christmas goodies. Year after year, Santa writes back, and a heartwarming relationship develops, until one year, the girl writes to her mother instead: Mom, are you Santa? Her mother responds to say that no, she is not Santa. Because Santa is bigger than any one person -- we bring him out through kindness to one another and the power of imagination. This transformative tale spins a universal childhood experience into a story about love, giving, and the spirit of Christmas.