I prefer saying minors/adolescents versus kids/children, since adolescence is an in-between from childhood to adulthood. Being the parent of 1 teenager and 1 child, it's obvious the former is closer to adulthood than the latter. (Plus, when I was a teenager, I felt like I was being talked down to or infantilized if called a kid/child.)
Anywhoo, as someone closing in on 31, I don't really consider someone an adult until they're 25ish. There's still a ton of maturity to be developed from 18 to 25.
So, I do agree teenagers in media need to be portrayed by minors/adolescents. Having adolescents play teenagers gives more realistic representation. Too many teenagers think looking or acting like particular characters is the goal, when those actors and the people who write the stories are adults. So obviously they're flawed representations.
Further, I think it's kind of an insidious tactic that allows minor-aged characters to be put in adult situations, justified by the actors are adults. Like, they're sexualizing this underage character, but it's fine because the actor is actually an adult? But that doesn't translate well from that universe to ours, which leads to over-sexualization (especially by adults) of actual minors today. Not to mention the grooming aspect, which allows adolescents to accept sexualization aimed at them from adults.
As for narrative examples of teenagers, that's a bit more difficult. Adult writers probably forget how to think, act, or speak like a teen, to some extent. lol