Saw this and couldn't help but respond as I live in Townsville.
Google 'The Strand' in Townsville. It is our main beach with heaps to do. You can swim at the rockpool with the kids which is a man made lagoon type thing of the beach. The water park is part of the stand. With picnic tables, parks BBQ's etc there.
The beach is great. It doesn't become stinger season until November so the stinger nets won't be up and the water is fine to swim in
I also recommend a day at Magnetic Island. Google it, and the biggest bay 'Horse shoe Bay' Plenty of stuff to do there.
Also maybe Billabong Santuary. An award winning zoo type place that has tonnes of Aussie Animals.http://www.billabongsanctuary.com.au/
Also Reef HQ is a MUST see.http://www.reefhq.com.au/
I guess the downside of our beaches is the sand is a bit grainy (like raw sugar) and there are no waves. But that is because we have the Great Barrier Reef at our doorstep.