BabylonJS 6 looks amazing - but I am curious to know what people use to help them place objects in a scene rather than doing it all through code? For example, the new version 6 demo that lets you throw a teddy around to knock things over, thats scene has hundreds of objects - can anyone tell me what tools were used to help put that scene together?
Maybe the Babylon.js editor can help you?
Regarding the playroom demo, objects are created and positioned by code because they all use thin instances.
In the case of the demo, the “base” meshes like the red cups, bowling pins, etc, were created on tools like Blender and 3DS, and then as Popov mentioned, we used thin instances to replicate the base shape many many times 
And for example, as placing each cube on a stack individually would be super boring, we made some formulas to calculate automatically where each one should go 
For me personally I “prototyped” each type of puzzle in the Playground and then added the code to the demo