My pet peeve. In graduate school we had professors, lecturers, working professionals etc constantly calling us students "kids" even though we were all 25+ yrs old. I believe this is a pretty American thing to always be infantilizing people.
"Baby" does not count because it's not German, and it can be traced back directly to imported pop culture (Movies). You are right about "Mädels", it's not exactly the same as "girl" though (rather girly) - you would never say "Mädchenabend", that's cringy.
In all American TV shows set in high school, the actors/actresses are all in their mid-20s. Ralph Macchio was in his 30s when he played the Karate Kid. It's altered people's expectations of how people look at certain ages.