Javascript override inherited variable using Modular Pattern

Question

Using the JavaScript modular pattern, I'm attempting to override a variable defined in the parent class, via it's children.

I've defined these classes as enclosures.

        var parentClass = (function () {
            var _tabsPerCall;
            var _nextCall;
            var _tabsArray;

            var loadNext = function () {
                var nextCallAmount = _tabsPerCall + _tabsPerCall;
                _nextCall = (_tabsArray.length - nextCallAmount) >= 0 ? nextCallAmount : _tabsArray.length;
            };

            return {
                get: function () {
                    return _tabsArray.slice(0, _nextCall);
                },
                clicked: function (tabIndex) {
                    if (tabIndex === _nextCall) {
                        loadNext();
                    }
                }
            };
        })();

        var child1Class = (function (parentClass) {
            var newObj = parentClass;

            newObj._tabsPerCall = 6;
            newObj._nextCall = 6;
            newObj._tabsArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

            return newObj;
        })(parentClass);

        var child2Class = (function (parentClass) {
            var newObj = parentClass;

            newObj._tabsPerCall = 5;
            newObj._nextCall = 5;
            newObj._tabsArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];

            return newObj;
        })(parentClass);

When I call childClass.get(), though, I get an error, stating that _tabsArray is undefined.

Both children would need to maintain different values for _tabsPerCall, _nextCall and _tabsArray.

Before, I was attempting to do it this way, but both children were sharing the same instance of parentClass:

            var childClass= (function (tabBtnBuilder) {
            tabBtnBuilder._tabsPerCall = 6;
            tabBtnBuilder._nextCall = 6;
            tabBtnBuilder._tabsArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

            return tabBtnBuilder;
        })(tabBtnBuilder);

Am I not overriding the parentClass properly?

I need both children to inherit from parentClass, but they need to maintain their own instances of the parentClass variables.