child.js

var sleep = require('sleep').sleep;

process.on('message', function (message) {
  console.log('message from parent:', message);
});

if (process.send) {
  for (let i=0, len = 100; i < len; i++) {
    sleep(1);
    process.send(`Hello-${i}`);
  }
}

launch.json

{
  // Use IntelliSense to learn about possible attributes.
  // Hover to view descriptions of existing attributes.
  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
  "version": "0.2.0",
  "configurations": [
    {
      "type": "node",
      "request": "attach",
      "name": "Attach",
      "port": 9999
    },
    {
      "name": "Attach to Process",
      "type": "node",
      "request": "attach",
      "processId": "${command:PickProcess}",
      "port": 9999
    }
    {
      "type": "node",
      "request": "launch",
      "name": "Launch Program",
      "program": "${workspaceFolder}/parent.js"
    }
  ]
}

parent.js

cProcess = require('child_process');
path = require('path');

const program = path.resolve('child.js');
// const parameters = ['--inspect=9999'];
const parameters = [];
const options = {
  execArgv: ['--inspect=9999'],
  stdio: ['pipe', 'pipe', 'pipe', 'ipc']
};

const child = cProcess.fork(program, parameters, options);

child.on('message', function (message) {
  child.send(`Hi-${message.split('-')[1]}`);
  console.log('message from child:', message);
});