If your husband works for Cathay, it would be very convenient for you guys to live in Tung Chung. Check out the
Caribbean Coast and other neighboring housing estates. The Caribbean Coast has a lot of club house facilities like swimming pools, bowling, reading area, Internet cafe, kid's area, mini golf, articial beach (to come), etc. There is quite a lot of open space around. Compared to Discovery Bay, it is much closer to the airport and much cheaper. For around 11000 HKD you can rent a three bedroom apartment with balcony and seaview. But there is definitely a larger expat population in DB.
By the way, do you really want your kid to learn mandarin? People in Hong Kong speak Cantonese, so if he learns mandarin at school, he would have a problem communicating with local kids.