S.B.
I know this sounds horrible but dishwashing liquid soap in the mouth. My little sister used to bite my cousin so bad she scarred his back. My parents tried everything the child psychologists recommended and nothing worked. One day my mom was doing the dishes and seen my sister about to bite my cousin and she just grabbed the bottle of dishwashing soap and squirted it in her mouth and let me tell you she never bit again. I don't know if it'd work for a child that age though. My sister was probably 4-5.