I haven’t read Bleach or Naruto so I can’t really comment on how those comics handle death. But I know quite a few kids who are about 10-11 years old who love Naruto. That sounds like about the right age when kids start reading and watching stuff that’s more violent.
I didn’t know what age group you meant in the first post when you just said “kids,” so I envisioned 7 year olds. I still think it’s okay to have deaths in comics aimed all all ages, just so long as you don’t glorify the violence or draw gratuitous details. Like, you can have big explosions, probably, as long as it’s really obvious your story is a fantasy and has no bearing in real life. Drawing terrorist planes crashing into skyscrapers is probably crossing a line when it comes to really little kids.
Also, I don’t think kids are smarter today than we were when we were kids. I work at public elementary schools and I strongly believe that kids today aren’t smarter - but parents today are certainly a lot dumber.