Short answer: B.
Here is why:
A might seem likely, but is actually incorrect because it does not show enough evidence to be anything more than a statement. It would more likely be a stereotype if the sentence was "All boys" or just "Boys" instead of "the boys", which refers to a specific group of boys.
B represents a family making boys do an activity. The answer as to why is not certain, but is likely because that is a "boys" thing to do.
C simply talks about a specific person, with no implication that their is stereotype involved.
D simply talks about the family success, with no stereotypical aspect involved.