Modest clothing for little girls and teens is available online being made by Christian, usually homeschooling families.
I have a 10 y.o. daughter and a 20 y.o. It’s still quite possible to buy decent clothing for the little one in the stores - clothing that is not more revealing than when I or my mother were growing up. I steer clear of clingy fabrics, writing across the backside, anything that emphasizes the non-existent bosom. Hand-me-downs from her cousin are edited - no “Apple Cheeks” jeans - what was her mother thinking? “Candies” brand - complete boycott there.
It’s much harder buying for teenagers. Even in church, even for funerals, the girls are wearing short tight skirts, night club shoes. They don’t know any better; they think that’s how you dress up. Again, their mothers SHOULD know better and lay down the law. At least maxi skirts have come into style in the last year.