I don't really have any advice. But, i will tell you that my son has eaten fuzz for as long as i can remember. He was diagnosed with PDD(ons) [Pervasive Development Disorder (otherwise not specified)]. It falls on the autism spectrum. But it basically means that he displays characteristics of but not enough to give a viable diagnosis. I assume that his diagnosis has something to do with him doing this. By the way he is now nearly nine and still does it.
I am not in anyway saying that you child has this issue I am just telling you what i have experienced.
It could also be a sensory need that he is trying to fill. Oral sensory or something. Call 1st steps and ask them if you can talk with an occupational therapist about it. They might let you do it without an evaluation. They might have tips or theories on why he does it.
sorry I don't have all the answers, but i hope this is a start.