Hello How Are You?.... I Have A Grandson Thats 21

hello how are you?.... i have a grandson thats 21 months old and he was taken to the hospital due to shaking barely being able to stand and he is off balance. the doctors at the emergency department drew fluid from his spine and also did a MRI on him and could not find anything but he was diagnosed with acute cerebral childhood illness could you please explain to me what that is and how long will it take for it to go away