Nine-year-old Daniel died in hospital on Sunday night . His eight-year-old sister Piper died on Sunday morning . They were both involved in a horrific car crash on the NSW Central Coast . Were travelling with elder brother , mother and grandmother . Elder brother William Kulk , 12 , is in a stable condition in Westmead hospital .
Nine-year-old William Kulk died in hospital on Sunday night . His eight-year-old sister Piper died on Sunday morning . They were both involved in a horrific car crash on the NSW Central Coast . Were travelling with elder brother , mother and grandmother . Elder brother Daniel , 12 , is in a stable condition in Westmead hospital .