Specifically, all passengers (including children) entering Hong Kong must fill in the health declaration form (that is, the health declaration form for Hong Kong residents) before arriving in Hong Kong, and show the completed declaration form to the border control personnel upon arrival. If the passenger fails to fill in the declaration form, he may be refused entry.
In addition, according to the regulations of the Hong Kong government, passengers who stay in Hong Kong for more than 14 days need to undergo COVID-19 inspection, and show their inspection certificates to border inspectors when entering the country. If the passenger can't provide the test certificate, he may be refused entry.
Therefore, if your child is going to Hong Kong, it is recommended that you fill in the health declaration form in advance and prepare the COVID-19 test certificate, so as to pass the border inspection smoothly when entering Hong Kong.