Question

Why would the author's son think there are 13 months in a year?

Answer 1

Because in the native tribal calendar there are 13 full moons in a year

Answer 2

In An Indian Father's Plea, the author's son, a 5-year-old boy named WInd-Wolf believes that there are 13 months in a year, not because he does not know how to count correctly but because he has been taught that in the native tribal calendar there are 13 full moons in a year and that there are actually 13 planets in the solar system.