This is a very good question. Fortunately, both Hong Kong and Singapore are very small markets. Thus there is much greater transparency and fewer layers of heirarchy.
I have lived and workedi n Hong Kong for over 2 decades. I also do business with Singapore.
First, is your material in English, Chinese, Both? That will make difference it terms of the market. The local market in Hong Kong will require Chinese language. The higher end of the market and the international schools can work with English. In Singapore, English will work.
I think there are several channels you can pursue.
Since 'youth' tend to go to school, you might want to do an outreach to the schools (probably start with the international schools in both countries and then move on to the better local schools).
There are also local community service organizations that range for Police sponsored youth programs to Rotary and Lions clubs that also have youth programs.
There are many other charitable organizations in each country that could potentially a good channel for your products.
Recreation clubs (Football Club, LRC, Cricket Club, etc) also have youth programs. They might be worth contacting.
I would suggest reaching out to as many of these sources as possible. The ones you contact might not be the right organizations for you, but they can suggest who else might be interested.
Despite the small size of each country, things are still done very much on a word-of-mouth basis. Few good directories of services - not like in the West.
Hope this is of some value. Good luck with your projects.
Should you want to discuss this further, I am available for a phone conversation.