Although the HK run is an option it may be quite an expensive one for a family. The first option I would check out is that of renewing the visas through the local Public Security Bureau. Going by Guangzhou regulations of the past (which may not have changed):
From the Guangzhou Govt site:
2. Visa Extension
"A foreign visitor who wants to extend his or her stay in the PRC or change the type or content of his or her visa should file an application with the relevant government agency in a timely manner according to the following procedures:
(1) Present his or her passport, visa and other required identification papers;
(2) Fill out the visa extension or visa change application form;
(3) Provide a certificate justifying the reason for the visa extension or change.
http://www.gz.gov.cn/publicfiles/business/htmlfiles/gzgoven/s3667/Or from an agency that charges a fee for processing a visa (uguide.org):
Renewal of L Visa
Renewal of L (Tourist) Visa:
Tourism Visa (L): Issued to those who enter China temporarily for leisure, family visiting or other personal affairs (multiple-entry is not granted for this category with an options of up to two entries).
L visa in China
If you enter into China on a tourist “L” visa with intent to stay beyond the validity period specified on the current visa, we can assist you to extend your current “L” visa. You can re-apply for a one month zero-entry or single-entry L visa for a maximum of two times per entry into China.
Documents required:
Passport with valid L visa
One 2-inch passport photo
Registration Form of Temporary Residence (from police station or hotel)
Processing time: 5 business days provided all materials for application are complete.
Years ago I had to organise this for a visitor and the 'Registration Form of Temporary Residence' was a basic form filled in by the local police station using information I supplied.
What thoughts on this as an option?