Over the past 20 years or so, my daughter and I have visited the majority of these locations in our home city of Sydney and close by areas.
01-20: Sydney Cove and Sydney CBD
21-28: Darling Harbour & close by
29-38: North-East along Sydney Harbour to Manly, then North to Palm Beach
39-42: East to Bondi Beach
43-54: West to Parramatta and beyond
55-68: South along the coast to Wollongong & beyond
69-74: West to Blue Mountains
75-80: North of Sydney
Some coastal suburbs have a surf beach and a calmer beach on the bay side, suitable for younger children (e.g. Manly & Cronulla beaches)