Hi SunnyD.
Well, I have to say, it's starting to get a little chilly. I'm not sure though if that's because I'm getting used to the warmer summer weather, so it seems colder now IYSWIM or not though (moved here last August).
The weather was fabulous from about Nov to the end of April and suddenly has got cold in the mornings and evenings, but warm during the middle part of the day. Wouldn't fancy the beach though.
I think you would still have a great holiday though, for most, it would be a holiday of a lifetime. If you wanted some beach & sunshine head a bit farther north for part of your break, to show the DC what a wide variety of climates there are.
There is heaps for your family to do though - my 2 DSS came out last month and loved every second, and they are 20 and 15 (I was expecting them to be a bit indifferent because they are cool teens, but they were thrilled to see the kangaroos, wallabies, snakes, Bondi Beach etc etc).
I'm sure some of the locals will be on soon, and they will be able to advise much better about the weather.