For tourist visa, must I have round trip return airticket booking record?

My little daughter,singapore citizen, soon 1 year old, is travelling together with my mother,china citizen,and planned to stay at my mother's home for more than 1 month in China. Since the return date is not confirmed yet, no return airticket has been booked. But I am sure I will get the return airticket whithin the entry permit valid date. Normally 3 months will be allowed for L type, right? any advice for this case? Thank you!