How to get the global/world position of a child object?

In threejs r89 you can just get the world position by Object3D.getWorldPosition. I don't know when it was added.

You can extract the world position like so:

var target = new THREE.Vector3(); // create once an reuse it

child.getWorldPosition( target );

target will contain the result.

EDIT: updated to three.js r.120