My 8month son can't sitting by himself.. he start crawling properly. when he is 3 4month he not able to hold his neck. after 5month he start holding neck. He copy my expression since 2month old. he is very active in all activities but he is not sitting. doctor said that is hypotonia but I don't understand that if it is hypotonia than how he crawling.. Even he specks at this age maa paa even his father's name ... please help me to understand this situation?