NodeJS: exit parent, leave child alive

i am writing an utility. One command of this utility is to run an external application.

var child_process = require('child_process');
var fs = require('fs');

var out = fs.openSync('.../../log/out.log', 'a');
var err = fs.openSync('.../../log/err.log', 'a');

exports.Unref = function(app, argv) {

  var child = child_process.spawn(app, argv, {
    detached: true,
    stdio: [ 'ignore', out, err ]
  });
  child.unref();
  //process.exit(0);
};

Currently:

$ utility run app --some-args // run external app
    // cant enter next command while app is running

My Problem is that if i run this command, the terminal is locked while the "external" Application is running.

But the terminal window shouldn't be locked by the child_process.

i wanna run:

$ utility run app --some-args
$ next-command
$ next-command

The external Application (a desktop application) will be closed by hisself.

Like this:

$ subl server.js // this runs Sublime Text and passes a file to the editor
$ npm start // The terminal does not locked - i can execute next command while Sublime is still running

You know what i mean ^^?