Harris and the narrator are both young, energetic, fun-loving boys. They are both highly imaginative and creative, and capable enough to be able to handle the myriad difficult chores that are part of growing up on a farm.
Harris is younger than the narrator; during the "Summer Remembered", he is nine while the narrator is eleven. Probably due to the circumstances of their upbringings, Harris is remarkably natural and uninhibited, saying exactly what is on his mind without a filter, and unfazed by running around in at times in near or total undress. The narrator, whose parents are alcoholics, has been shuttled around from relative to relative for some time, and is understandably more reserved in his actions. When he arrives at the Larsons' farm, he "(holds) back...the shyness kicking in" (Chapter 1), but he is quickly put at ease by the Larsons', and especially Harris's, friendly, straighforward manner.
The narrator has the tendency to think things through much more than Harris. He is better at reading and writing than his younger cousin, who has to have his sister inscribe his letter for him because he "don't write so good" (Epilogue). The narrator is much more inclined to conform to social norms, while Harris chafes at rules of any kind, complaining, "Rules...every time you turn around there's something you can't have or something you can't do" (Chapter 7).