Depends. As a teenager I started wearing thongs because:
a) they meant no panty lines
b) my girlfriends wore them and I at least wanted to know what it was like
c) they made me feel more womanly/grown up. I've always been a huge fan of pretty lingerie because the only people who ever see it are myself and my partner, which makes it like a fun little secret

I didn't wear them to show anyone but myself, and I actually find the string ones uncomfortable so I've always worn the fuller ones. They were also ALWAYS worn under pants (i.e not under a skirt, esp. a flowy one) and never peeked above the top of my jeans. Because of all of this, my mom never had a problem with my wearing them and I think that if I had a daughter with the same approach, that would be completely fine by me. My main concern would just be that she's not wearing them to flaunt them and that like any other types of panties, her underwear stays under her clothes (I also have a personal issue with exposed bra straps ).

And apparently thongs pose a bit of a health risk if you wear them all the time (you can double check this on google!), so I would encourage my daughter to wear varied styles of underwear. I only wear them when I go out, or have a night in less

When she's only enough to start picking out her own underwear? Yes.
This is no different an issue than when to start wearing make-up. Women wear make-up. Young girls are women in training, why is it wrong for them to wear it then?(I'm refering back a couple decades here)

Standard panties can be considered just as, if not more, erotic than thongs. Does that mean she can't wear standard panties then? When girls reach their early teens, it's in their nature to do whatever they can to be/act as a grown-up. Preventing them from doing it is not going to teach them how to be a grown up the right way. The best thing is to be there for her and guide her with responsability. less

Stifling kids sexuality isn't going to change the actions of creepers. Creepers are creepers and that's it.

I'm not encouraging anyone to buy their kids frilly underthings, but if you actively show kids that sex is wrong (not only with words, but with actions like freaking out over a thong or other harmless yet sex-related item) there's a chance they're going to internalize it and turn it into some kind of sexual dysfunction later on. Learning healthy attitudes about sex happens slowly over a lifetime, you can't just suddenly flip a switch at an "appropriate" age and "let" them begin to explore that arena.

And like Pussy Galore said, this is a surprising reaction from this community particularly. I can recall pretty kinky fantasies I was having at age 7, an age when a lot of Western society is generally scandalized by any show of sexuality. Children are humans, and humans are sexual creatures. We don't have to encourage them to be blatant and showy in their sexuality, but we do kinda need to just get over it. less