Careful, He Might Hear You(1983)

The bitter struggle between two sisters for the love of a little boy.

Abandoned by his father after his mother dies, young PS lives in suburban Sydney with his aunt Lila and her husband George. While they lead a modest existence, PS is happy with them. However, his contentment is derailed when Lila's wealthy sister, Vanessa, returns from England and takes an interest in PS.