My daughters are 9 and 12 (almost 13... 7/5 I'll be the mother of a teenager! Ugh!) And both are allowed to wear tankinis but nothing more revealing than that. I guess I'm fortunate in that both girls have a strong sense of modesty and don't really want to show a lot of skin. My older daughter is, however, entering that clevage-bearing phase where she'd like to wear lower-cut tops. I tell her fine, she can wear it all she wants in her room, but to get out of the door she has to wear a tank top or cami under the shirt. I guess this works for both of us because the layering look is popular and it covers up her clevage (father's genes kicking in here - bigger than mine! So not fair! Grumble...)
I just don't think it's appropriate to allow (or worse, to encourage) your pre-teen daughters to be viewed as sex-symbols. That happens soon enough as it is, and we don't need to rush things along. What's wrong with pink frills and girl-y clothes for as long as they'll wear them? They're only young once, and everyone involved with raising little girls should enjoy it before it's gone.
Okay, I feel like crying now. Those days are long gone and I miss them terribly right about now.