If you don’t have access to a sandpit you could buy a bag of sand and work on a tray. Alternatively you can work on a smaller scale using clay or plasticine.
It’s best to start with an island and a lake as these are recognisable to most children (in Australia anyway!).
Your child may made the connection and ask to decorate the island with sea creatures and shells.
Here we are at the local park … never to old to play in the sandpit!