My son is 5 and does the same thing. He was diagnosised with ADHD last year and I think it has something to do with the need for stimulation. He also chews on whatever he can find (trach on the floor, wrappers, placstic, ect...). Hes not actually eating the items, so its not PICA. We have just kinda tried to accomidate his need by allowing him to chew gum. His preschool teacher last year made rubber necklace (of sorts) for him to have in class. My suggestion is just to try and accomidate his need with a more "approprite" item- cause repeating "get your shirt out of our mouth" a million times a day is frustrating to everyone and not helpful.
