There is Just Juniors Mini Movers on Thursday afternoon in the Phase two club house for two and a half to three and a half years.
It is a gym based movement program not exactly playgroup, it is only 45 minutes so may not be what you are after.
Also there is Music Together which is a 45 minute music program in Phase two Gold Coast, Aegean Coast and also starting at Grand Pacific Heights.
Again, they are NOT playgroups but activities for a three year old. You can call 2815 5866 if you are interested.
New Generation Kindergarten in Tuen Mun and also Jing Jing Kindergarten in Tuen Mun run playgroups and pre nursery classes, I am not sure of the numbers but they may be helpful to you in offering something for a three year old, they appear to be popular.