Actually, Blue mountain is a very good place to go with the family as there are different kind of cable cars, trains etc. You can take a look to three sisters and echo point. There are small towns around. We did visit various towns and have dinner there.
For Hunter Valley, there is a local Zoo named Hunter Valley Zoo. It is a small one but I like it very much as you can get very close to the Kangaroo (red one), Sheep, etc. There are big lawn near the Chateau. My kids just ran around the lawn happily. You can't find a similar one in HK.