This seems to be a reiteration of the same point: you believe that if somebody finds the work environment hostile, it's ok to pressure them to leave. You're really not seeing anything wrong with that?
I'd also question your belief that "the girls" (who are, I take it, 8-12 years old) are ok with it. Go talk to some people in the field who have had a few jobs but aren't stereotypical. E.g., gay, female, or black. Ask them if they've ever laughed at something that made them uncomfortable because they wanted to fit in and felt unsafe doing anything else. Because you're ok with pushing out somebody if they don't like the joke, guess what: if they don't like the joke, they'll still pretend to you that they do.
I'd also question your belief that "the girls" (who are, I take it, 8-12 years old) are ok with it. Go talk to some people in the field who have had a few jobs but aren't stereotypical. E.g., gay, female, or black. Ask them if they've ever laughed at something that made them uncomfortable because they wanted to fit in and felt unsafe doing anything else. Because you're ok with pushing out somebody if they don't like the joke, guess what: if they don't like the joke, they'll still pretend to you that they do.