Hun there are a few medical conditions that could cause kids to eat unusual things. I would get him checked out by a doctor and maybe look into OT? My daughter has sensory integration disorder, sometimes kids are affected by one sense, or two or a whole gammat. One of hers is oral factory, where she puts everything in her mouth... if there is nothing else than its her hair. Another is texture, sometimes they need more textures in their mouths... I was told with her to only offer her crunchy snacks, so an apple, carrots, bread sticks etc... Its helped us tremendously cutting down on softer foods and offering her crunchy healthy food 6-8 times a day. Seriously, if we have soup for tea, she has croutons in her soup as well as toast soldiers. She will also have a gingernut biscuit (hard one of course!) for a snack after dinner, rice crackers for arvo tea.... etc etc to ensure she gets enough of the crunchy stuff. She has an apple in the car on the way home from school just to keep that up.

BUT she never consumed the things she chewed on... just held them in her mouth. So maybe get your little one checked out and make sure he doesn't have anything that is causing it... its called Pica, and go from there.