There are definitely kids with ADHD for whom medications definitely help. However, from my personal experience, it seems like it is a little "over diagnosed". But I could be wrong - this is just my very limited experience.
Are there any material (video or similar) showing how an average ADHD kid behaves today vs. 20 years ago?
It is both over and under diagnosed. Teachers are likely to refer any highly disruptive kids for screenings, while ignoring less disruptive kids.
However, being disruptive isn't a particularly good proxy for "has ADHD" and someone without ADHD that is referred has a higher chance of being diagnoesd with ADHD than someone with that is not referred. This results in a lot of kids who end up being treated who shouldn't and plenty of kids who go untreated who could benefit.
Are there any material (video or similar) showing how an average ADHD kid behaves today vs. 20 years ago?