I'm not sure if Capone was showing strictly jealousy about Jimmys son being normal. I think he was more intrigued by the patience and tenderness Jimmy showed to his son teaching him to tie his shoelaces and was having a moment of self reflection. Very different than the way Capone acted around his family in Chicago. That moment didn't last long though and he quickly slipped back into his tough guy demeanor telling 'Frankenstein' that his wife is a ***** when he asks how she has been.