Think about it. If you, as a mom and adult, were going to wear a skirt or dress and planned to be on the monkey bars hanging upside down, wouldn't you rather have shorts on? That's all it is for me. I'm not much of a skirt/dress woman myself, but if I do wear one I do make sure my undies aren't showing and I teach my girls to do the same. I don't tell them not to climb on the monkey bars, nor do I insist that they not wear skirts if they're planning on climbing the monkey bars, but shorts underneath are a good compromise for me. I view my job as a parent as guiding my kids toward adulthood. This is one step on the way for me.
I like Lands End bathing suits for my girls. They're feminine w/o being skanky, even the bikinis. Podsnap, I think bathing suits are very regional. I have a mom acquaintance who came from a region in the US where bikinis were the norm for moms, too, but when she came here she got a tankini because she saw that not as many moms wear bikinis. Some do, though, and I think she would have been fine to wear one, but for whatever reason she didn't feel comfortable. I prefer the boy shorts (not board shorts, but the tight ones) so I don't have to shave because I'm too d@mn lazy and I don't like the skirts. I know moms and girls in my area who wear bikinis, tankinis, competitive suits, skirt suits, board shorts and rash guards. The pool culture in my area is actually very focused on swim team so there are lots of competitive suits in our local pools. In my area there's definitely nail polish, but not so much the other products, hair gel, etc.