Home Return Permit for a kid

Hi,
My son was born in Australia while I was not a PR but my husband was a citizen of Australia. In 2018, my son was granted a tourist visa to China but not this time. However, we are just told that he needs to get an HKID, and then Home Return Permit to travel to Zhuhai for two days. My son is only 6 and not supposed to get HKID, what should we do?