Hi Mollie,
Sai Kung is a lovely area. Your son would be K2 here, there are quite a few pre schools here in the Sai Kung / Clearwater Bay area. Some are more international - these are the two ESF kindergartens; Abacus and Wu Kai Sha, Woodlands, Leapfrog, SKIP and Garden House. There are also some local ones like Sun Island, but I don't know much about these - maybe someone else can advise? I suggest you arrange to visit some of them when you arrive. If you are planning on sending your youngest to AISHK it won't matter which one you attend in terms of entry, whereas if you are thinking about ESF then one of the ESF kindergartens may be more appropriate as they get priority for interview and places are tight in this area. I hope this helps.