I would recommend starting with Scratch as many have suggested. It is easier to pick up than other options, and kids can always move onto something more complex later on.
There is also Arcade MakeCode (https://arcade.makecode.com) which is similar to Scratch.
Some of my son's projects:
- Godot: https://arandompsi.itch.io
- Scratch (rather old): https://scratch.mit.edu/users/codewithliam/projects/