pipe not being read by subprocess?

I want to run node.js as a subprocess and feed it input. Using C, here is some sample code of mine that does that.

The issue I have is that although the subprocess's stdout is still directed to the terminal, I see nothing after having fed the subprocess stdin a print 'Hello World' line. Even if I fflush() the pipe, I see nothing on output. However, if I close the pipe's input, then the 'Hello World' appears on the terminal.

The subprocess seems to simply buffer - why is that? I would like to eventually redirect the subprocess stdout to another pipe and read it in from main().

int main(int argc, char* argv[]) {

  int toNode[2];

  pipe(toNode);

  pid_t child_pid = fork();
  if (child_pid == 0) { // child

      // close write end
      close(toNode[1]);
      // connect read end to stdin
      dup2(toNode[0], STDIN_FILENO);


      // run node executable
      char* arg_list[] = { "/usr/bin/node", NULL};
      execvp(arg_list[0], arg_list);

      fprintf(stderr, "process failed to start: %s\n", strerror(errno));
      abort();
   }
   else { // parent

      FILE* stream;

      // close read end
      close(toNode[0]);

      // convert write fd to FILE object
      stream = fdopen(toNode[1], "w");

      fprintf(stream, "console.log('Hello World');\n");
      fflush(stream);

      //close(toNode[1]);


      waitpid(child_pid, NULL, 0);

   }

return 0;   }