A good question.
A local answer.

Check Transperth's current payment options for each route before your first trip.

Check today's group-ticket rules and child fares; a price quoted in a much older forum thread is not reliable.

Check the station entrance and walking connection for the specific line on the travel day.

If the luggage or transfer feels awkward after a long flight, compare a direct taxi or rideshare fare for two people.

The ferry is a short scenic link but may not run when you want to return; plan an alternative way back before the evening.

Perth Underground and Perth Station are connected but serve different rail lines; allow time to walk between platforms.

Use Transperth's current planner for the Perth-to-Fremantle route and today's fare method; old prices can mislead.

Choose one beach per outing if transfers make a combined day too long.

Pick your destination within Kings Park first, then use the current public transport planner for that entrance.

For Rottnest or a regional tour, book the departure first and then plan the connection from your hotel.

List only the journeys you will actually take without the car, then compare the current Transperth fares and payment options for each traveller. An old forum post may describe a fare rule that has changed.

CAT routes are designated central-area services; numbered routes are part of the wider Transperth network. Check the current map because a stop near your hotel may have both.