Installing NPM dependencies for child projects that use Grunt.

Gruntfile.js

module.exports = function(grunt) {
  // ...
  
  grunt.loadNpmTasks('grunt-install-dependencies');

  grunt.registerTask('install-npm-dependencies', 'Installs NPM dependencies for child projects that use Grunt.', function () {
    var projects = [];

    grunt.file.expand('project/*').forEach(function (path) {
      if (grunt.file.isDir(path)) {
        grunt.file.recurse(path, function (abspath, rootdir, subdir, filename) {
          if (filename === 'Gruntfile.js' && projects.indexOf(rootdir) === -1) {
            projects.push(rootdir);
          }
        });
      }
    });

    projects.forEach(function (project) {
      grunt.config.set('task.install-dependencies.options.cwd', project);
      grunt.task.run('install-dependencies');
    });
  });
};

Uses grunt-install-dependencies.