ok.js

//start script
var subLayers = app.activeDocument.layers.getByName("parent").pageItems;

var smallestParentArea = 100000000;
var parentSmallest = [];
var smallestChild = "no smallest child found yet";
//loop through all sublayers to find children
for(var i = 0; i < subLayers.length; i++){
    var smallestChild;
    var childContainer = subLayers[i],
        childContainerArea = childContainer.width * childContainer.height;
    print("#################"+childContainer.name+" : CHILD compare ###################");
    //compare all subLayers to other sublayers    
    for(var j = 0; j < subLayers.length; j++){
        var parentContainer = subLayers[j],
            parentArea = parentContainer.width * parentContainer.height;
        // check to see if it is comparing to itself, skip if it is
        if (i != j){
            // check to see if childContainer is in another layer
            print("-----"+parentContainer.name+" : PARENT compair -----"); 
            if(isIn(childContainer, parentContainer) &&  childContainerArea < parentArea ) {
                if(smallestChild =="string"){ smallestChild.name };
                print(">> TEST :: "+childContainer.name+": SMALLEST CHILD // area:"+childContainerArea+" // "+smallestChild+" (index: "+j+") USED TO BE SMALLEST CHILD");
                smallestChild = childContainer;
                smallestParentArea = parentContainerArea;
                parentSmallest.push(parentContainer);
                print("parent is:"+parentContainer.name+"\n");
            }
        }
    }
}

     
function isIn(child, parentItem){
    var childVB = child.visibleBounds,
        childLeft = childVB[0],
        childTop = Math.abs(childVB[1]),
        childRight = childVB[2],
        childBottom = Math.abs(childVB[3]);
    var parentVB = parentItem.visibleBounds,
        parentLeft = parentVB[0],
        parentTop = Math.abs(parentVB[1]),
        parentRight = parentVB[2],
        parentBottom = Math.abs(parentVB[3]);
        
    $.write(child.name+" :  [ left: "+childVB[0]+" , top: "+Math.abs(childVB[1]) +" , right: "+childVB[2] +", bottom: "+Math.abs(childVB[3])+"]  \n\n" );
    $.write(parentItem.name+" :   [ left: "+parentVB[0]+", top: "+Math.abs(parentVB[1]) +" , right: "+parentVB[2] +" , bottom: "+Math.abs(parentVB[3])+"]  \n\n" );
    //return true if child is in parent
    return childLeft >= parentLeft && 
           childTop >= parentTop && 
           childRight <= parentRight && 
           childBottom <= parentBottom;
}

//check what the smallest container is:
$.writeln("!!! "+smallestChild.name+" is the smallest conatiner. it's position is: "+smallestChild.visibleBounds+"\n \n"+"its parent(s) is/are: "+parentSmallest);

//clear variables because ES is stupid sometimes
var childContainer = null,   
    childContainerArea = null,
    parentArea = null,
    parentContainer = null,
    isSame = null;

yuh.js

for(var i = 0; i < subLayers.length; i++){
    var smallestChild;
    var childContainer = subLayers[i],
        childContainerArea = childContainer.width * childContainer.height;
    print("#################"+childContainer.name+" : CHILD compare ###################");
    //compare all subLayers to other sublayers    
    for(var j = 0; j < subLayers.length; j++){
        var parentContainer = subLayers[j],
            parentArea = parentContainer.width * parentContainer.height;
        // check to see if it is comparing to itself, skip if it is
        if (i != j){
            // check to see if childContainer is in another layer
            print("-----"+parentContainer.name+" : PARENT compair -----"); 
            if(isIn(childContainer, parentContainer) &&  childContainerArea < parentArea ) {
                if(smallestChild =="string"){ smallestChild.name };
                print(">> TEST :: "+childContainer.name+": SMALLEST CHILD // area:"+childContainerArea+" // "+smallestChild+" (index: "+j+") USED TO BE SMALLEST CHILD");
                smallestChild = childContainer;
                smallestParentArea = parentContainerArea;
                parentSmallest.push(parentContainer);
                print("parent is:"+parentContainer.name+"\n");
            }
        }
    }
}