Hi
Dont' worry.... my daughter is 9 years old and does exactly the same thing - and chews sleeves too. She only started doing it about 6 months ago and I know for a fact she isn't worried about anything, she's very laid back, doing well at school, has good friends etc and happy at home. I have asked her why she does it, she says she's not sure - 'I just do'. I think it's just a habit, like chewing finger nails etc. and am just waiting for her to grow out of it. I used to suck flannels as a child for a while at about her age - it hasn't affected me in anyway.