when my fiance was around that age his mother was constantly having to buy him new shirts, especially long sleeved ones.. he would chew and suck on the ends of his sleeves and if he had short sleeves on he would take the collar of his shirt and put that in his mouth and chew on it, she said no matter how many times they told him to stop it didnt matter but he eventually grew out of it... on another, weirder note, his younger brother somewhere around that age, if they were eating some kind of meat for dinner he would chew it for a really long time and then just keep it in his mouth and later on in the day they would catch him chewing something and eating it and it would be his meat from lunch/dinner! how weird is that lol.. he grew out of that too dont worry