Plot-important scene change that bothered me...

So, I was watching this movie in class, and I noticed that one of the major plot points was cut. In the book of this movie, the blue man turned blue after drinking silver nitrate because he had a problem with incontinence. In the movie, he says that he is a troubled child, and it shows him being hit by someone. I don't get why such a scene would be cut in the movie adaptation if it was important to the plot, yet they have one of the people in the war say that someone stained their pants. A few G-rated shows have incontinence scenes (Magical DoReMi and Rugrats, to name 2), but why would this movie cut the incontinence scene in the book that was very relevant to the plot?