I teach piano not keyboard. The piano is an instrument rich in sounds. You will need a good quality acoustic piano and tune it every year. If you wish to buy a second-hand piano I am always happy to help you make a selection by trying a piano for you before you buy.
It is understandable that you may want to try out lessons for a few months before investing in an instrument and for this time a keyboard will suffice. I will be teaching technique right from the first lesson and keyboard makes a very disappointing sound and very little technique is required to play one.
The latest digital pianos are very good. They have the advantage of making a pleasant sound and the touch is similar to a piano. They are a better choice than a keyboard or old piano, but for the higher music grades an acoustic piano will be necessary.
Lucky the child who has a new piano from the start! The best pianos to buy in Australia for children are possibly K Kawai or Yamaha.