Do I have to show proof of return ticket

I would like to stay 6-12 months with my son and his family in China. I understand I have to apply for a multi entry visa with 90 days stay each entry, I will have to leave for a day or 2 each time.
My quistion is this: Do I have to have proof of a return ticket and date when I apply?. I am not sure how long I will stay.
Francis