What kind of government organizations can I reach to for more information for the service about children with disabilities?

Not at all.

Thank you so much for your useful information.

You can refer to the following websites to get the information you are interested in. For example,
(1) Department of Health
https://www.dh.gov.hk/eindex.html
(2) Education Bureau
https://www.edb.gov.hk/en/index.html
(3) Hong Kong Examinations and Assessment Authority
https://www.hkeaa.edu.hk/en/
(4) Social Welfare Department
http://www.swd.gov.hk
(5) The Equal Opportunities Commission (EOC)
https://www.eoc.org.hk/