I do think sometimes cartoons for 8 ages and up should feature some darker themes. I mean, nothing gory, sexual or extremely unsettling, but maybe some elements that could challenge their naiveté. You know, a way of explaining to these kids that the world can have really bad stuff, and that people sometimes are not up to good...
By the way (and trying to get back on topic), I've recently seen a series of videos talking about the history of Magical Girl anime:
Mahou Profile, from
ErynCerise Youtube channel. If you're interested in learning more (or, most likely, -considering you're magical girl experts- remembering stuff) about the genre that has united us here, check it out! It's a great documentary-like series, well narrated and highly detailed. Here's the first episode:
View: https://www.youtube.com/watch?v=SUt6PperTKI
There are some more, and each one so far has focused on one anime at a time. We'll see how long this girl goes with this series!