Police were called to a home on Jamieson Avenue, Baulkham Hills, at about 5.20am today.
They found a 10-year-old boy, a 13-year-old girl, a 16-year-old girl, and a 46-year-old woman, all with stab wounds.
They are all believed to be known to each other.
They were treated at the scene and taken to hospital in a stable condition.
An investigation is underway.
It’s understood police are not looking for any other person.
