My Hero Academia is also violent, but it's a bit less graphic than Demon Slayer, and it's themed around super heroes/villains so the concept may be more approachable for a child. It's one of my personal favorites, but fair warning: The themes do get somewhat more mature as the show goes on.
If your kid has an interest in science, Dr. Stone could be a great fit. Contains some violence, but it's mostly about a super genius recreating modern technology using primitive resources after an apocalypse.
Another one in the science vein, Cells at Work tells the story of anthropomorphic cells living and doing their jobs in a human body. Again, some violence, but it's mostly cartoonish and shouldn't be much of a worry for a kid.
~~Fairy Tail is also a good choice, especially since its audience skews younger than the other recs I've given here. It follows a group of wizards at a famous guild as they take on quests and go on adventures. Very kid-friendly with a huge backlog of episodes.~~
On second thought, maybe give Fairy Tail a miss due to the fanservice. I apparently blocked all those scenes from my memory when watching as a kid.
Oh damn, you're definitely right about Fairy Tail. It's been so long since I've watched it I completely forgot about all the fanservice. It's bizarre though, because if it wasn't for that it'd fit right in with other "Saturday morning" kids anime like Yu-Gi-Oh and Pokemon