there are loads of classes available on hk island.
you can try any of the "gym" classes, JWT, panda junction, little gym, my gym...i believe they take babies under one.
if you want to go further afield than hk island, there's more...
I highly recommend PEKIP! They have classes in Wanchai and also in Stanley. We started when my second one was 5 months and we "graduated" when she turned 1. I will definitely take PEKIP again if ever I'll have #3.