Does anyone know of something similar, but for aircraft and/or drones? I’ve been 3D printing model aircraft with my 8-year old but would be great to take it to the next level.

[Ardupilot|https://ardupilot.org/] maybe? It's for controlling the drones, but I think it has simulators as well.

There is a game on Steam where you can design and fly your own aircraft. Would be fun to then try to 3d print the successful ones. But I can't remember the name of the game, sorry.

Kerbal Space Program?

No, its more aircraft oriented.