Regulations Governing the Detention of the People of the Mainland China Area and the Residents of Hong Kong and Macao Article 7

Upon application, permission may be granted for detainees to keep their younger children under the age of three (3) with them in a detention center.
中文原文 大陸地區人民及香港澳門居民收容管理辦法第7條
受收容人請求攜帶未滿三歲之子女者,得准許之。

English translation for reference only; the Chinese text prevails. Not legal advice.