S.G.
My son, now age 21 years old would act as if his right hand and arm were paralyzed. He would not use his right hand for anything. If he needed two hands it was usually left hand and mouth. Never right hand.
My oldest daughter (17 years old) was better. She would use her right only if she absolutely needed to. When her doctor asked her why she didn't use her right hand she said it was broken. Hahaha We asked her to explain and she said that the right hand doesn't work good enough. Both of my Lefty's are fine and have no motor skill delays.
What is really weird is watching a child who is ambidextrous. She is fine also but when she was young she needed something for both hands at all times. She even sucked both thumbs at the same time.