[Sharky1973]

I'm unsure whether the Lizard Island people do diving nowadays although they certainly should. Lizard is in relatively easy steaming distance of the Cod Hole which is pretty well known. Actually, have a look here:
http://www.lizardisland.com.au/great...r-reef-diving/

On Lizard you will really be restricted to this operator (the island is privately owned, used to be by P & O but perhaps not so today).

If you can, catch one of the small planes from Cairns to the island (you'll probably have to do that anyway). The low level flight over the GBR is simply spectacular.

Now the bad news: you are coming well into FNQ's (Far North Queensland's) "Big Wet" which I would usually always advise people to avoid at all costs, but it seems that you're committed now.

The Big Wet often includes nasty things like Cyclones and I can assure you that you haven't seen "wet" until you have shaken hands with one of ours.

As for Cyclones, think New Orleans or Cyclone Tracy which simply flattened Darwin:

http://www.ntlib.nt.gov.au/tracy/

I'd advise you to tell your youngest to avoid FNQ - actually FN anywhere in Oz - between now and May. Our winter, your summer, is the best time to see FNOz.

Cheers