Horse & Pony Books:
(BILVER [AUSTRALIA] 1983)
ILLUSTRATED BY CHRISTINE ALDERTON
SUMMARY: Historical story set in Australia just after the Second World War. Margaret, Christopher and Jane Barton live on a large sheep station in New South Wales. They are looking forward to a summer riding their ponies when they are joined by two English children and a refugee called Pieter. All six have a number of adventures together.
Reasonably easy to find in Australia, hard to find in the UK and USA. Prices tend to vary a lot.