When the kids are little, it can be hard to go off into the bush, as they get tired, start complaining and all the fun stops there.
A great place to ease into the bushwalk idea and still have a wonderful day, is to set off to West Head in the Ku-Ring-Gai Chase National Park. Parking will cost you $11 but after that, all is free.
Park near the Lookout, and make sure you take little ones to the toilets in the carpark as there are none down on the beach.
Spare some time to potter around the lookout - spectacular views of Lion Island and Barrenjoey Lighthouse are sure to please. There is also a great brass map of the bays and inlets, which is useful to point out the maze of waterways in Sydney.
Then head off to the bush track, down to Resolute beach. There are lookouts along the way, on the well maintained stair track. There is a 'waterfall' crossing, which from younger children provides much excitement. For everyone else, it's a scenic, easy bush walk, that takes about 12 minutes, down to the beach. As with all bushwalking, suitable covered shoes are recommended, and don't forget a hat and some water.
The beach is stunning and rarely crowded. It's small, with some large rocks to climb and recline on, watching the yachts sail past.
Gentle waves lap the shore, so it's a suitable swimming spot for little ones. Make sure you bring plenty of water and bear in mind there is not a lot of shade, so be well prepared with the sunscreen and think about the time of day you arrive.
Once you decide to head back, that doesn't have to be the end of the adventure. If the kids are keen to explore, there are a few other easy walks (10 minutes or so to the Red Hands Cave to see Aboriginal cave paintings) or you may want to head back up to the picnic area for lunch or a barbeque.
The trick is to plan your day, and the kids will soon learn that the walking is only half the fun, and often the rewards for a little effort are sublime.