We used to put our toddler at Kidscorners when he was 18mths - check out this link
www.kids-corner.com.hk. We joined the Baby Talk session which we found was good but my son at 18mths then could not really keep still and was more interested in the toys, tables and stools around the classroom.
Also now that my son is 2yrs he has been attending Zenith Kindergarten and Intl Nursery at Tin Shui Wai - they have a branch in Yuen Long as well. They also have playgroups for under 2yrs. Maybe you can give them a call and enquire about their playgroups on 2808 0993.