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.
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)
Answer: To show the strength of their friendship and show how much they loved each other, which is what that whole song was about.