I think this thread is going a bit off topic tbh. The OP hasn't said she doesn't want to ever talk to her dd about stuff, she just doesn't want her wearing crop tops!
so all this talk about ignoring periods etc is coming from people's own stories of their own parents and has nothing to do with the OP question as such. Mums who want to delay crop tops are not doing so out of ignorance, I'm sure if her dd was developing etc and needed support then she would let her wear them!
I also wouldn't let dd wear a crop too (she's 8 half) but that doesn't mean we haven't talked about periods etc as we have. I started at 9 so well aware dd would be young too. My dd has no breast buds etc so for me, she's fine with a vest. To be honest all this talk about kids being aware of their bodies and becoming self conscious, my dd wouldn't have a clue! None of her friends are like that yet as only year 3. if the OP dd is like that then I understand why she doesn't want to go there til she needs to.
I absolutely agree the op should ensure her dd wears something as it's not fair for her to change without something, but a vest would be fine. To be honest, I think a crop top highlights breast buds or smaller boobs much more than an actual vest due to the elastic at the bottom whereas a vest kind of skims them. A vest also covers more of the stomach area which I find kids are much more self conscious of!
If they are of size to need support then of course, but the OP hasn't said that. Neither has she said she is afraid of her growing up etc! She just doesn't like the idea of a crop top when her dd doesn't need one!
There is a time when kids need them for support etc or when vests simply become out of fashion but I don't think 8 has to be that time. I'm only 37 and I remember being in crop tops for only a short period and then it was bras.
I have to admit, its easy for me at the minute because no one in dds class wears them and I may too have to reconsider due to peer pressure :(