scale, transformation, position, parent object confusion

Hey there,

I am a bit confused regarding the position settings in Blender.

I have some objects which I set as childs into a parent object to scale them and move them all together. (Is there a better way todo so?)
Already did this to the parent and the childs got scaled and moved too.
After scaling and moving I realized I forgot one object. So I put it inside the parent.
Now the size and Position don’t fit anymore so I decided to take the scale of an other child and apply it to the object.
Now I want to equal the x axis of one of the child objects with the forgotten object and realize it seems to have a totally different coordinate system in which it seems to live. The 0 position is different then the ones from the other objects.

What exactly happens there? How can I reset this? I just want to use the global coordinate system.
Any ideas? In my opinion a child object should take the parent center as 0 position. But it seems not so simple?

Try reading these; http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Coordinate_Spaces_in_Blender
http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Parenting

There is an article around somewhere that explains this in great detail …I’ll post link when I find it.