Wendy and Her Lost Boys -- The Lost Boys 1987

Originally Posted on AO3 under the same username

Wendy is the lost boys' kid sister. They look out for her and she looks out for them, but seeing as she's a human, there is only so much she can do to help out with supernatural messes between college semesters.

A mysterious new girl and her family took up residence in Santa Carla two months ago, drawing Wendy's eye as the pair tested the waters and awkwardly flirted, resulting in Wendy finally asking the other girl out.

Wendy is excited and extremely nervous at the prospect of going on a date with the girl she's been crushing on. The only problem -- it's Wendy's first date. What happens when the boys try to take Wendy's mind off her impending date, resulting in them meeting her mystery girl, Ellie. They soon find there is something different about her and they are not sure what.

Or

The lost boys are extremely protective when it comes to the safety of their Wendy and are reluctant to let her go out with just anyone, especially when that someone is clearly hiding a secret.