smallestChild.js

//start library

function MyLayer(input) {
    this.doc = app.activeDocument;
    this.myLayerIndex = input || 0; 
    this.myLayerItem = this.hasLayerIndex() ? this.doc.layers[this.myLayerIndex] : false;
    this.subLayers = [];
    //this.visibleBounds = this.myLayerItem.visibleBounds;
    // push pageItems to SubLayer constructor/class
    for (var i = 0; i < this.myLayerItem.pageItems.length; i++) {
        var pageItem = this.myLayerItem.pageItems[i];
        //var visibleBounds = this.myLayerItem[i].visibleBounds;
        this.subLayers.push(new SubLayer(pageItem));
    }
    this.width = this.myLayerItem.width;
    this.height = this.myLayerItem.height;
};

MyLayer.prototype.hasLayerIndex = function() {
    return this.myLayerIndex <= this.doc.layers.length - 1;
};

function SubLayer(input) {
    return this.pageItem = input;
    return this.visibleBounds = this.visibileBounds;
    //this.top = this.visibleBounds.top;
} 

SubLayer.prototype.isIn = function(parentItem) {
    var parentVB = parentItem.visibleBounds;
    $.write(this.name+" : "+this.pageItem.left+" left, "+this.pageItem.top+"top, "+this.pageItem.right+"right, "+this.pageItem.bottom+", bottom \n ");
    $.write(this.pageItem.name+" : "+parentVB[0]+" left, "+parentVB[1] +"top, "+parentVB[2] +"right, "+parentVB[3]+", bottom \n" );
    
    return this.pageItem.left >= parentVB[0] && 
           this.pageItem.top >= parentVB[1] && 
           this.pageItem.right <= parentVB[2] && 
           this.pageItem.bottom >= parentVB[3];
};
*/

smallestChildOOP.js

#target illustrator

//start script
var subLayers = app.activeDocument.layers.getByName("parent").pageItems;
var smallestArea = 100000000;
    
for(var i = 0; i < subLayers.length; i++){
    var smallestContainer;
    var currentLayer = subLayers[i],
        currentLayerArea = currentLayer.width * currentLayer.height;
    //print(currentLayer.name+" : "+" i: "+i+"\np height: "+currentLayer.height+"\np width: "+currentLayer.width+"\np VB:"+currentLayer.visibleBounds);
    for(var j = 0; j < subLayers.length; j++){
        // check to see if it is comparing to itself, skip if it is
        if (i != j){
            var compareLayer = subLayers[j],
                compareArea = compareLayer.width * compareLayer.height;
            //print("     C "+compareLayer.name+" :             "+" j: "+j+" \n             c height: "+compareLayer.height+"\n             c width: "+compareLayer.width+"\n             c VB:"+compareLayer.visibleBounds);
            
            // check to see if currentLayer is in compare layer
            if(isIn(currentLayer, compareLayer) &&  currentLayerArea < smallestArea ) {
                print("TEST :: "+currentLayer.name+" is smallest layer and its area is: "+currentLayerArea+" // "+smallestContainer.name+" used to be smallest area");
                smallestContainer = currentLayer;
                smallestArea = currentLayerArea;
            }
        }else { $.writeln(subLayers[j].name+" = "+subLayers[i].name+" compare skipped"); }
    }
    print("################# end of compare ###################");
}

function isIn(child, parentItem){
    var parentVB = parentItem.visibleBounds,
        parentLeft = parentVB[0],
        parentTop = Math.abs(parentVB[1]),
        parentRight = parentVB[2],
        parentBottom = Math.abs(parentVB[3]);
        
    var childVB = child.visibleBounds,
        childLeft = childVB[0],
        childTop = Math.abs(childVB[1]),
        childRight = childVB[2],
        childBottom = Math.abs(childVB[3]);
    
    $.write(child.name+" :  \n [ left: "+childVB[0]+" , top: "+Math.abs(childVB[1]) +" , right: "+childVB[2] +", bottom: "+Math.abs(childVB[3])+"]  \n\n" );
    $.write(parentItem.name+" :  \n [ 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("!!! "+smallestContainer.name+" is the smallest conatiner. it's position is: "+smallestContainer.visibleBounds+"\n \n");

//clear variables because ES is stupid sometimes
var currentLayer = null,   
    currentLayerArea = null,
    compareArea = null,
    compareLayer = null,
    isSame = null;