junior BM dresses for flower girls?

so my FG will be a month shy of 8 years old at the wedding. That being said, people are suggesting junior BM dresses instead of FG dresses which i am totally in agreement with..BUT

I dont know how this dress will look as a junior BM dress. The woman said it would have thick straps, but I don't know how the body would be...do you think it's not a trumpet at all?

Has anyone had experience with this?? Were the dresses age appropriate??