We started with scratch and made a very simple game (asteroids-like). My kid then wanted to make a platformer, so I built a basic one for them and let them add stuff. It was kinda crappy and janky, so I found a template on Godot and removed a bunch of stuff to get what they wanted.
Boom, a couple hours of effort from my end they're building maps with the included tileset. They feel empowered without feeling overwhelmed.
They still don't know how to make a game (they're 10 and 7 respectively), but they have interest and may be willing to learn this summer.
So do that. If you're stuck, watch a few YouTube videos about first projects and follow along until you're ready to do it with your child.