Ok I heard that with the z axis it's possible to organize what objects are in front and what are behind. But when I use z=100 it only makes it smaller or bigger(one of the two not sure at the moment)? How do I go about adding children to the background?
What you heard is actually quite incorrect. The z property does not change the depth of an object. You must control the depth using setChildIndex, or addChild/addChildAt.