According to the guidelines of the Department of Health, if a child is sick:
Notify their parents / guardians and ask them to bring the sick child to the doctor as soon as possible
Isolate the sick child from others
If the situation is critical, send the sick child to a nearby The Accident and Emergency (A&E)
Prohibit children with infectious diseases from going to school
To prevent the spread of infectious diseases, sick children should stay at home and not go to school. When to return to school depends on the nature of the disease and depends on individual circumstances. Here are some general recommendations. If in doubt, please contact the District Offices of the Department of Health.
Prevention of Communicable Diseases in Schools
https://www.edb.gov.hk/tc/sch-admin/admin/about-sch/diseases-prevention/index.html
How to approach when your child is sick
According to the guidelines of the Department of Health, if a child is sick:
To prevent the spread of infectious diseases, sick children should stay at home and not go to school. When to return to school depends on the nature of the disease and depends on individual circumstances. Here are some general recommendations. If in doubt, please contact the District Offices of the Department of Health.
Prevention of Communicable Diseases in Schools
https://www.edb.gov.hk/tc/sch-admin/admin/about-sch/diseases-prevention/index.html