I found one here. It's pretty ugly with all the stuff they added on to it, but the basic shape should get the job done. You can also do a google search using the terms children's ski mask knitting pattern and children's balaclava knitting patterns. Both terms are used interchangeably. I seriously don't think I would go to that much trouble for a body costume that they'd only wear one day. You might be better off with a black or other solid color sweat shirt and sweat pants. You can paint it with temporary paints that wash out or temporarily tape cutouts on the suit. This jogging outfit can then be reused by your kids.