When Voldemort asked her to check if Harry was dead and she realised he was, in fact, still breathing, Narcissa seized her opportunity. ... Narcissa may have concealed the truth from Voldemort to save her son, but she inadvertently helped Harry to victory in doing so.

Did the Malfoys save Harry?

Draco did help save Harry, Ron, and Hermione by not identifying them to Death Eaters, which is a huge moment, but the most stand-out moment is when Draco is supposed to end Dumbledore's life. Planned all along by Snape and Dumbledore or not, Draco could not find it in himself to end a life.

What did Narcissa Malfoy whisper to Harry?

In a whisper, she asked if Draco was alive. When Harry replied quietly that he was, Narcissa betrayed the Dark Lord and asserted that Harry Potter was dead. She knew the only way her family would be reunited was as part of Voldemort's conquering army, thus proving she loved her family more than she supported Voldemort.