
Wainwrights is a very good food and if it suits you pup, which it sounds as though it is then i wouldn't go changing thier food around.
Lots of puppies eat grass roots dirt and all sorts, so I wouldn't worry too much, unless they are swallowing stones with it. Perhaps replace them with a stuffed kong to take thier mind off it or do some training etc to distract, but i am sure they will grow out of it in thier own time.