Piping data from child to parent in nodejs

I have a nodejs parent process that starts up another nodejs child process. The child process executes some logic and then returns output to the parent. The output is large and I'm trying to use pipes to communicate, as suggested in documentation for child.send() method (which works fine BTW).

I would like someone to suggest how to properly build this communication channel. I want to be able to send data from parent to child and also to be able to read data from child to parent. I've started it a bit, but it is incomplete (sends message only from parent to child) and throws an error.

Parent File Code:

var child_process = require('child_process');

var opts = {
    stdio: [process.stdin, process.stdout, process.stderr, 'pipe']
};
var child = child_process.spawn('node', ['./b.js'], opts);

require('streamifier').createReadStream('test 2').pipe(child.stdio[3]);

Child file code:

var fs =  require('fs');

// read from it
var readable = fs.createReadStream(null, {fd: 3});

var chunks = []; 

readable.on('data', function(chunk) {
    chunks.push(chunk);
});

readable.on('end', function() {
    console.log(chunks.join().toString());
})