start /b cmd /c %~0 2>nul 1>&2
Assuming I haven't forgotten a crucial part, this will open a new instance of the saved batch file in the background of the current file. They will share the same output console, and It's very complicated to stop them, but thats how you thread. I would recommend going with the above answer and doing something like
for %%A in (1,1,4) do start batch.bat
Which should open 4 separate instances of batch.bat.
Do a search for snake.bat on this site, (it's a link to a different forum) as an example of how it works.