dist/claygl.es.js
function (callback, context) {
        var _children = this._children;
        for(var i = 0, len = _children.length; i < len; i++) {
            var child = _children[i];
            callback.call(context, child, i);
        }
    }
function (callback, context) {
        var _children = this._children;
        for(var i = 0, len = _children.length; i < len; i++) {
            var child = _children[i];
            callback.call(context, child, i);
        }
    }
function ( callback , context ) { var _children = this . _children ; for ( var i = 0 , len = _children . length ; i < len ; i ++ ) { var child = _children [ i ] ; callback . call ( context , child , i ) ; } }
Traverse all children nodes.

**WARN** DON'T do `add`, `remove` operation in the callback during iteration.

@param {Function} callback
@param {Node} [context]
Traverse all children nodes .