Overriding the "extend" method in backbone, also see http://stackoverflow.com/questions/12356531/how-does-one-override-the-extend-method-in-backbone/12356533

gistfile1.js

var enableChildTracking = function (Klass) {
    var old_extend = Klass.extend;
    Klass.__children = [];
    Klass.extend = function () {
        var That = this;
        var result = old_extend.apply(That, arguments);
        That.__children.push(result);
        result.__children = [];
        return result;
    };
};

var A = Backbone.Model.extend({});
enableChildTracking(A);

B = A.extend({}, {className: "B"});
C = A.extend({}, {className: "C"});
A.__children.map(function (child) {return child.className}); /* == ["B", "C"] */