My 3 year-old son "loves" swimming after just 1 week "intensive swim programme" at Australian International School HK in Kowloon Tong, taught by Australian trainers. Their approach is quite different to the local squads. My 6 year-old sons also learn there and improved dramatically in just 2 weeks during summer!
I think it is no good to learn swimming at 3 years old becuase:
1. difficult for the coach to communicate
2. the body structure is not ready
My son started to learn at age of 4 1/2(2 years ago) for those 1:4 class and now manage to swim 4 styles (at 6 1/2 years old). This is much much better than my expectation.
Let me share my experience, I found selection of coach is very important. Some coach can make the learning very interesting but some is terrible. We have bad experience with the first coach as the coach is only pulling my son arround in the pool (with 3 floating broads) for one hour and never learn to swim. The he get a cold and we have to stop the swimming class for 2 weeks. The second coach is really good. No swimming aid with a lot of encouragement. My son can put his head under the water in the first lesson and also like to attend the class.
Above is their website, you need to complete the registration online, by first setting up your login. It is a bit late to join the summer intensive course now because it ended in July. You can still see if there is any course suitable for your child. The usual term course is once a week for 9 or 10 weeks. It would be better if your child can understand english even if he doesn't speak too well, as the medium is in English.