Baby Chewing and Teething: A Developmental Stage
Sometime between the age of 2 and 4 months, most newborns make the exciting discovery of chewing on their own fists. They quickly learn the coordination to get toys, pacifiers and even their own toes in there, as well. Freud called this the "oral stage" of infancy and it continues to some degree until 2 years of age.
This developmental stage is one of the first ways, in addition to vision and hearing, that your child explores her environment. And the chewing also can help to break through those first precious teeth and ease the pain associated with the teething process. So the only thing you should discourage is when your baby gets old enough to put things in her mouth that are dangerous, either a choking hazard or a poisoning hazard.