Discovery Bay gets a lot of stick from people who don't know much about it. It's 10 years since I lived there, but went back last weekend and it hasn't changed much. I think the atmosphere is unbeatable for families - laid back, relaxed, no traffic (you probably know they have this bizarre system where there are only golf buggies and the occasional bus), 100% safe, really nice environment with the hills rising just at the back. Also the beach is nice, and is just a couple of hundred yards from most housing. If you can swing one of the family houses there it's so much better than apartment living - you might get a garden! (that's something you can't get 99.99% of places in HK!). There's a supermarket as good as any in HK, plus every other everyday shop you need in the Plaza. The residents' club has great sports facilities, gym, nice pool, all very family-orientated and very sociable. Your wife will have lots of other mums and kids to socialise with.
Yep, transport's an issue - the ferry is the ONLY way in and out, but it's a fast air-con ferry every 20 mins 24/7. Using the ferry is not cheap, but that's the only drawback I can think of for a family moving to DB. Believe me after a few weeks you'll really appreciate the relaxed Mediterranean feel of DB - HK is such a hectic, crowded place it's fantastic to live in a chilled-out place away from traffic, noise, crowds. Go for it!!
PS No, I'm not sponsored by the DB company, honest!