Gradually restrict the amount of time mum is in with them (she will probably appreciate this, as their nails will be sharp and scratching her teats and tummy). Let her in to give them a quick feed and clean up, and then let her out again. She will also start to clean them up less, still licking them but not eating the poo. Done over a few days, her milk will gradually dry up. If her milk is not drying up after a week or so, epsom salts will help, but not usually necessary. As long as she can get in and out herself, she will probably do so. No need to take her completely away from them, if necessary put a puppy pen up so she can see them and visit a few times a day, or let them out so she can play with them but is not 'trapped' by them where she can't get away.