Margaret River with kids Caves, a jetty train and a fudge window

Start with the jetty. It runs 1.841 km into Geographe Bay, the longest timber-piled jetty in the Southern Hemisphere. The walk out is lovely. The walk back is the same distance and feels twice as far to anyone under eight. That's what the little solar train is for.

At the far end, the Underwater Observatory goes 8 metres below the surface, down a spiral staircase, so the kids get to see the sea from the inside. Tours take up to 44 people and depend on the weather, so book ahead on the jetty's own site. Prams are welcome on the jetty walk but not on the train or in the observatory, so bring a baby carrier if you're doing either.

On the foreshore by the jetty, Sea Play on the Bay is a nautical-themed adventure playground built for a mix of ages and abilities. Water features are worked into the design, so someone may well go home damp.

For the smallest, the Toddlers Playspace on the same foreshore has a rail theme, built around a restored ganger trolley. Aquatastic, an inflatable water park, sits right next to the jetty. Check its own site for when it's open and who can go on what before anyone gets their hopes up.

Every car has one: the kid who knows more snake names than you do. Discover Deadly, on Wildwood Road at Carbunup River, is for them. It keeps more than 40 species of reptiles, amphibians, arachnids and birds, in enclosures indoors and out.

Keepers give talks and run feeding sessions through the day. Check the times when you arrive and plan the visit around one. Watching something have its lunch is the bit they'll describe in the car.

Country Life Farm has been family-run since 1989, and it's a petting farm in the old sense: you're there to feed things. Rabbits, guinea pigs, kangaroos, llamas, alpacas, goats, sheep, donkeys, ponies and cows can all be fed by hand.

When the animals have had enough of you, there's a large indoor playground, a merry-go-round, row and pedal boats, and bumper cars. The bumper cars are for age 6 and up, and younger kids can ride with an adult, which is how you end up in a bumper car.

Ngilgi Cave is the one you explore at your own pace, 36 metres underground, with a guide in the main chamber to answer questions. Inside there's an optional crawl tunnel for kids, and a nature play area waits at the final stop. There are 350 steps, with rest platforms. Nobody needs them on the way down.

Allow about an hour and a half. Babies go in a front carrier: backpack carriers aren't allowed, and prams only work on the above-ground Ancient Lands Experience. Afterwards, the Yallingup Foreshore playground overlooks the beach, with a surf-shack cubby, swings, shaded barbecues, beach showers and toilets.

On Margaret River's main street, the Fudge Factory has a window straight into its kitchen. Through it you can watch each batch being mixed, poured and cut. For anyone under ten it's the best show in town, and the hardest one to walk away from.

The family business has been making fudge by hand here since 1999. The flavours run from vanilla and salted caramel to Strawberry and Cream and a Fairy Fudge, with rocky road on the side. Parking is free in town, with a few timed bays on the main street.

Finish underground again, on Caves Road south of town. More than 10,000 fossils have been found in Mammoth Cave, including remains of Australia's long-extinct megafauna, and a 50,000-year-old jawbone of a zygomaturus is still set in the cave wall. Mention that at the entrance and the questions will last the drive home.

It's self-guided, with an audio guide, and takes about an hour. A gently sloping boardwalk and 370 steps take you through the chambers. Babies ride in a front carrier, which keeps a hand free: backpack carriers aren't allowed, and prams can't go inside. When you come out, the visit carries on with a walk through Boranup Forest. Book ahead in the school holidays, and ask about the Megafauna Nightstalks, a special tour the Capes Foundation runs at Mammoth.