This post is getting a bit old but hey, what the heck. I'll answer since no one else has.
Can't talk for Sai Kung/CWB but I did live in DB for 2 years so will chip in my 2 cents. DB is a great place for families with millions of mummies and kids running around.
But, you should be aware that even if you live in Discovery Bay, you are not entitled to free access to the clubs. In fact the clubs are quite restrictive and you have to pay a lot if you want the full works (pool, gym, classes, etc). Nothing, and I repeat nothing, is free in DB!
A lot of families hang out around The Plaza, which is the sort of central meeting point by the ferry pier surrounded by restaurants and what not. (Or, to be more precise, the parents tend to sit around with beers from the 7-11 while the kids run wild!) People are ALWAYS hanging around there.
There are lots of classes for kids though, they have signs up everywhere. Art, ballet, Chinese lessons, you name it.
As for the golf cart -- Not sure how many millions you have in the bank but you will need roughly HKD 1 mill if you want to get a golf cart of your own (and yes, I'm not joking!). Most people rely on the internal buses, which run in time with the ferry, or they just walk if they live close enough. It is good for getting exercise! If you live close to the ferry then you are close to the Plaza and the supermarkets (10-15 min walk). If you live on the other side of DB, like WAY on the other side, it isn't practical to walk. You'd have to take a bus for sure.
The ferry is really quite comfortable, about 30 mins to Central. Much better than the horrid noisy busy crowded MTR. And on the ferry you are guaranteed a nice comfy seat to read/sleep/use WiFi/drink beer etc etc. But, be warned your life will start to revolve around ferry timings to make sure you don't miss them.
For me the green, quiet environment in DB outweighed these minor inconveniences/restrictions, and I don't even have kids. I just liked having green mountains around me, and being able to walk out the door and go hiking. I also like how you can hop on the little old boats that go to other nearby islands and bays, such as Mui Wo, Peng Chau, and what not. Makes for good weekend outings too.