Or maybe you just have a lot of exposure to the niche CW audience?
I don't get this - Superman doesn't need to be returned to kids, he never left them. Why is it always "a character is for us (adults) or kids" with some fans? Superman can and should have stories for kids, for adults, and for both. This just for one or the other idea will make him more obscure. He should have an animated theatrical movie for kids, a live action Marvel styled movie for families, a cartoon series, an adult Black Label title, an R-rated Joker style Lex Luthor movie, and some edgy PG 13 DTV movies. Give us a Superman for every audience. I mean, it's worked for Batman so far.
1. Superman doesn't really belong to kids - Superman belongs to everybody. He belongs to kids, he belongs to 30-something adults like me, and he belongs to old bastards like you too. That's part of the greatness of Superman. Let's not do him the disservice of thinking he's only for a certain age group of the populace. There should be more Superman kid content, but that's not all there should be.
2. The Marvel being an outlier to the grim dark stuff is wrong. Pretty much every era of pop culture is full of extremes. How many people who loved The Big Bang Theory also enjoyed JOKER? Aquaman and Game of Thrones? The MCU and Breaking Bad? People aren't all about the gritty stuff, nor the lighthearted stuff, neither dominates pop culture. People love both extremes in fiction when done well. The 70s gave us Superman The Movie, Star Wars, and I think The Godfather and Dirty Harry. The 80s had Indiana Jones, the Goonies, Back to the Future, and more horror slasher films than you can shake a machete at. Neither dominates.