Collision detection problem

From looking at the difference sections, this seems to be the correct one.
Any moderator feel free to move it to the correct section, if it's posted incorrectly.

My problem is that I have a mesh cube with box collision on,
BUT this object has several child objecs which are mesh planes.
Adding a RigidBody to allow for collision detection is impossible,
as it seems to count the children as part of the parrent object.

It's really annoying it does that by default, can you turn the thing off
which count's in the children for collision?
...or do something else to make it work?

 

Were you ever able to find a solution?