Actionscript noob having problems

i’m using actionscript 3 and i’ve made2 movie clips named mcRect and mcchild(instance name is child2_mc) and i double click it to go into mcRect’s scene and type the code into an new layer that says “root.child2_mc.x = 0;” but i get an error saying “1119: Access of possibly undefined property child2_mc through a reference with static type flash.display:DisplayObject.”