You don’t need a special license to open a Playgroup, you just need to register your business.
According to the EDB’s reply, Playgroup does not fall within the scope of the Child Care Services Ordinance and therefore does not require a special permit or licence. Private educational institutions only need to be registered as a business in order to open classes and enroll students.
However, it should be noted that if your Playgroup provides playgroups that aim to promote the intellectual development of young children or develop physical and social skills, it will not fall within the scope of the EDB’s regulation.
If a child is accompanied by a parent, he or she may circumvent the restriction on “child-keeping premises” under the Child Care Services Ordinance.
Child Care Services Ordinance (Cap. 243) https://www.elegislation.gov.hk/hk/cap243!zh-Hant-HK