Steps to reproduce:

1. Create a new project
2. Create an empty game object and attach 'Rigidbody' to it
3. Turn off gravity in the rigidbody
4. Create 2 new spheres and make them as children of an empty game object
5. Move one sphere away from another a bit
6. Press play
7, Drag one of the spheres in the scene
8. Select the parent and look in the inspector window

As a result, the parent's position slightly changed after moving one of the children in the scene

Note: Turning off the children colliders will not reproduce this issue anymore

Reproduced on: 5.6.0b2, 5.5.0p3, 5.5.0f3,