Medical question - mentally defected children?

For starters i work with special needs children and the words mental defect altho probably not meant bad in any way arent really anice way to describe someones mental issues...would u like to be referred to as "defected".....anyway it does sound like your nephew has some problems and i wouldnt just ume his parents arent aware of this its likely they do and are dealing with it privately....however it may be an idea for the Mother or father of the parents to broach the subject with one of their kids about their grandchild...are they also aware of this?