There are lots of buildings in HK that are fantastic for kids and would not require you to have a car. I really suggest you take a look round before getting too enamoured with any one place. Places to consider that are like the Repulse Bay (big, lots of kids, good facilities) are; Parkview, Bel Air, Manhattan, Pacific View. I would also strongly recommend Stanley. It's got a pretty good community feel, there are loads of kids and for the same price you'd pay at the Repulse Bay you should be able to get a bit more space, perhaps a bit of garden or roof terrace etc. You also have the added bonus of being able to walk to everything you need without feeling like you are so 'separate' from the rest of the world, something I would feel living in the RB.
Please don't worry about your children being lonely in HK. It is one of the easiest places for them to make friends particularly on the Southside, where lots of expats live.
Whatever you decide rents have come down a lot here, even in the Repulse Bay so don't let them tell you otherwise.