I have a 5 year old girl, and she also has not worn any tank tops or bikinis, even as a baby. I didn't want her seeing pictures of her as a baby in a bikini and asking "Why was it okay for me to wear those THEN, but not NOW?" Kids can spot hypocricy (even if it's hypocricy only by their own interpretation) and I wanted to avoid those fights (cuz I know I gave them to my parents!). We don't wear tank tops or bikinis because we don't. Period. Of course I'll teach about modesty and all that as well, but there aren't going to be seperate modesty standards presented by age or gender. My sons don't wear tank tops either, and if the trend of boys wearing their pants around their ankles is still around when they hit the teen years (Please, God, NO!) they won't be allowed to do so, whether they're showing skin or not.
And I will bring the blind by a way that they knew not; I will lead them in paths that they have not known: I will make darkness light before them, and crooked things straight. These things will I do unto them, and not forsake them.
My Family Blog: http://morekidsthanhands.blogspot.com/