Other mistake: In one of the opening scenes where the boys ride to the baseball game, the fishermen they pass make a rude comment towards them. In response, you hear Joe ring his bicycle bell and see them flip the men off. The bicycle has no bell.
Other mistake: In the second baseball scene, Joe is sitting on the bench next to one character with the number 8 and Simon, who is on Joe's other side is also number 8. Two players on the same team would not be the same number.
Answer: I think they let Simon go because he was sick at the time.