index.js

'use strict';

var spawn = require('child_process').spawn,
    es = require('event-stream');

// helper method to return whether an array or string contains a value
var contains = function (source, value) {
  return !!~source.indexOf(value);  
};

var childrenOfPid = function (pid, callback) {
  var headers;

  // callback is a required argument
  if (typeof callback !== 'function') {
    throw new Error('childrenOfPid(pid, callback) expects callback');
  }

  // stringify the PID in case it's a number
  pid = '' + pid;

  es.connect(
    spawn('ps', ['-A', '-o', 'ppid,pid']).stdout,
    es.split(),
    es.map(function (line, mapCallback) {
      // this could parse a lot of Unix command output
      var columns = line.trim().split(/\s+/);

      if (!headers) {
        headers = columns;
      } else {
        var row = {};
        var headersCopy = headers.slice();

        while (headersCopy.length) {
            row[headersCopy.shift()] = headersCopy.length ?
                columns.shift() :
                columns.join(' ');
        }

        return mapCallback(null, row);
      }

      return mapCallback();
    }),
    es.writeArray(function (err, processes) {
      var parents = [ pid ],
        children = [];

      processes.forEach(function (err, process) {
        if (contains(parents, process.PPID)) {
          parents.push(process.PID);
          children.push(process);
        }
      });

      callback(null, children);
    })
  )
  .on('error', callback);
};

if (!module.parent) {
  childrenOfPid(process.argv[2] || 1, function (err, data) {
    console.log(data);
  });
}