That's a good point! From my homeschooling group, I know a few mixed-race families, and a *lot* of families that have a mix of kids (sometimes some are biological and some aren't, but sometimes the kids are all adopted but just have different looks). I remember one mom talking about the looks she got when she (white) and her daughter (black) had their hair done the same way. And apparently the most common comment is, "Are they yours?" Which, while I could see somebody having reason to ask, has got to be painful for the kids to hear over, and over, and over, and over, you know? Just to complicate things, my husband and I are open to considering fostering or adoption at some point, and we'd be open to any race or sex, so we *could* end up with all sorts of questions being asked! Not to mention if we foster or adopt a boy after having had all girls biologically. I can only imagine the comments we'd get. But it's true in the end that it wouldn't make us decide to stick to adopting/fostering only girls of our race, so we'll have to deal with it if it happens.
I'll admit that I'm sort of assuming that if we have a fifth, it'll be a girl. While theoretically it's about 50/50, you definitely can have a tendency towards one sex or the other. Maybe I've just read Pride and Prejudice too much!
I definitely don't want to say anything that would come back to haunt me if we *did* have a boy at some point. So I can't go with the "I'm a specialist!" or "he'd look silly in the hand-me-downs!" type of comments, even if I think they're utterly hilarious (and I'll have to share them with my SIL, who has 3 boys and is definitely done, I think she'd love these ideas).
As for girls and sports, sure, girls can/do play sports. I have this theory, though, that when you have a household of all one sex, you have an increased tendency towards "girly" or "boyish" behavior, because that tends to be what the kids have in common. One girl might like dolls and theater, another like LEGOs and dolls, another like dolls and riding bikes, but that means that they all have playing dolls in common, so there's an increased tendency to play dolls because you see everybody else doing it, and everybody can do it together, etc. Versus my SIL's household which has a lot of guns and shooting and sports and superheroes.