Continuity mistake: Near the end of the movie, Barney walks out of a huge pile of hay. He shakes and brushes all of the hay off, but a few seconds later he has a bunch of hay on the top of his head again. (01:03:10)
Continuity mistake: In the marching band scene they all have long shadows, and then suddenly they have no shadows at all.
Continuity mistake: In the beginning, when the kids are riding to their grandparents', at first their father is driving the car. After passing the Apple Day Festival, their mother is suddenly driving.
Answer: To show the strength of their friendship and show how much they loved each other, which is what that whole song was about.