"Une fille" vs. "Une jeune fille"
In French class (admittedly many years ago) we were taught never to refer to a female child as "une fille" because it generally referred to a prostitute; we were taught always to distinguish the noun by preceding it with "jeune". Has this changed?
Well, "une fille" still refers to a prostitute (even if it is more common to say "une prostituée" to speak in a polite manner) but it sounds a bit old now: I had to read a book in French class where they used "fille" to talk about prostitutes but it was written in the early 1880s... So yes, you can use "une fille" to refer to a girl. If you want to specify that she is young, then use "une jeune fille".
I wish I helped you, I am not a french teacher so I could be wrong. Bon courage to learn French!