getChildAt with totalFrames

I have a number of childs added in a movie, I’m using a for() loop to see if childs have reached the end of their individual timelines. If so, they’ll be removed. childs have been put in array ‘obj’ . Now when I trace

obj[j].currentFrame and obj[j].totalFrames

it results neatly in their momentary frame point and total frames value. But when I trace

getChildAt(j).currentFrame and getChildAt(j).totalFrames

I get error
“1119: Access of possibly undefined property currentFrame through a reference with static type flash.display:DisplayObject.”

I need to go with the for() loop through the getChildAt(j) since obj[j] won’t work. Why? ->
Once childs are deleted then the stacking order obj[j] won’t remain value ‘j’ anymore … depth levels are changed and getChildAt(j) won’t point anymore to obj[j] … getChildAt(1) will be obj[2], then after next remove obj[3] and so on.

So the milion dollar question, what’s wrong with syntax

getChildAt(j).currentFrame

??
anyone?
P