"The implant may destroy..." (fairly clear) "...in that ear..." (where; ie. the specific ear which still has residual hearing) "...the residual hearing..." (what may be destroyed) "...the child may have." (describes the residual hearing) Simply put, the "where" has been shuffled to a different part of the sentence instead of being placed at the end. This is just for clarity.

I guess it is about an hearing demage. This implant could be dangerous for children's hearing!

The sentence is just plain wrong. It doesn't make sense to me.