Is your HK permanent id still valid? How about your son, is he a HK permanent ID holder?

My ID is old but I am going to renew it when I return. My son does not have an ID, otherwise won't require a dependent visa.

you can send his Hong Kong Visa Application Form(https://www.travelchinaguide.com/embassy/pdf/hk-new.pdf) to HK Immigration directly with following documents:
1. Photocopy of the personal particulars page of the passport or other travel documents which has at least 6 months remaining validity.
2. Two recent passport photos (2x2, front view);
3. name, address, and telephone number of the school where your son is admitted;
4. the admission notice from the school in which the applicant is going to study;
5.certificate of education;
6. if the applicant is under 18 years of age, documents containing consent of parents or legal guardian must be provided;
7. financial sponsorship.
Money order or cheque of 52 US Dollars payable to the Government of the Hong Kong Special Administrative Region clearly indicating that the payment shall be made by a bank in HK. ( $30 for visa fee, $22 for the returning mail of approval by the HK Immigration Department.) In addition, prepare a self-addressed return express envelope. Please be advised that your payment does not guarantee your application be approved. As the approval of the said visa must be decided upon by the HK Immigration Department, and generally, it takes at least 21 days to obtain a visa to HK.