Can 6 y.o. child (Australian citizen) in China as tourist apply student visa? Mum has China passport

Desperate help me please? It's a complicated situation, my sister-in-law & my brother are divorcing. In the process of the divorce, my sister-in-law decided to bring her son (Australian citizen) to China while my brother went on business trip overseas & without my his permission. Even though my nephew didn't want to go but as a six year old, he can't do anything. She is a PR of China's citizen who has Australian Permanent Resident visa. She threaten us (child's aunts, grandparents & father) that we won't see him again and going to make him studying primary school in China. She lied to us that she only will go for holiday. We only found it out when she already checked-in at the airport & called us. We are very sad, extremely stressed & worried to death now. Can anyone tell me whether it is possible for my nephew to get the student visa without his father's permission? Or to convert his tourist visa to student visa while the child is already in China? My sister-in-law is unemployed now. Also, does anyone where do we have to go to get help to bring the child back to Australia? We were hoping that visa rejection will bring the child back here. Your help & answer is very much appreciated to lessen our stress level.