I have created to spheres: one smaller sphere is sitting inside a larger sphere. By setting the outer sphere as parent and the inner sphere as child, I can move them together by only attempting to move the outer parent sphere.
I then turned on the particle system using a collection containing the two spheres and the box "whole collection" checked. This creates particles looking like my original two spheres, one sitting inside the other.
After converting the particles to objects, however, the parent - child relation between the outer and inner spheres seems to be lost, i.e. when I move the outer sphere of one of the spheres created from particles, the inner sphere does not move along with it. What am I doing wrong? Thank you, Hidari