There are a number of children who chew especially the clothes they are putting on. You notice that when that child is doing something that requires concentration, that is when he/she chew. But when playing the chewing is not in the mind. My son used to chew his school shirt or his handkerchief and I did the following till he stopped.
Never force him/her to stop
Don't ever tell the child to stop chewing because to him/her, it is the best thing ever. Instead, try to look for alternative ways to help in stopping the habit.
Include hard to chew foods in the diet
Always give the child hart foods to chew. Hard foods include the carrots, sugar cane, crackers, and apples. Make sure the child chews the above things at least once a day.
Have a sensory diet
You can consult an occupational therapist to guide you on the sensory diet to the child. A sensory diet helps in reducing the need for chewing and also regulates the child's sensory system.
Provide a safe outlet to chew
When the children feel like they need to chew, they can have anything near them to chew. In the process, they may land on harmful things that contain chemicals. So before telling them to stop chewing clothes, have a safe alternative to what they can chew.
Include oral activities
Let your child do things like drinking through straws, blow cotton balls and even holding some things with their mouth for some seconds. These activities provide oral sensory feedback.