Your morality.

Of course, in this discussion, we all act like we're good people! But in reality, if we were in the crusader's shoes, we would have a completely different mindset. Therefore, it's pointless to discuss what people from the 21st century would do in such a situation. Naturally, a crusader in such a situation, like most warriors, would hardly think about who his prisoners were. This boy might grow up and take revenge later, which is why wars often involved killing children.