NodeJs flow error

I am new to NodeJs and I have the following code using the nimbel library

function createNode(callback){
    exec(console.log("2"),callback);
}

flow.series([
    function(callback){
        console.log("1");
        for (i=0;i<2;i++){
            flow.parallel([
                function(callback){
                  createNode(callback

);
                }
            ],callback);
        }
    },
    function(callback){
        console.log("3");
        callback();
    }
    ]);

I want the output from the console to be 1,2,2,3 but the last function that outputs 3 is not being called any ideas ?