Cindy Crawford’s getting real about her brother dying at a young age ... saying her dad wanted a boy, so she and her sisters felt like they should’ve died instead.

The legendary supermodel opened up about her survivor’s guilt in a new episode of the “Kelly Corrigan Wonders” podcast ... telling the host about the aftermath of her 3-year-old brother Jeffrey’s death from leukemia.

CC says her father, John, had finally got his baby boy ... so when Jeffrey died, Cindy and his other daughters “felt like, well, it should have been one of us” adding the household felt weird for years after.

Looking back, Crawford says she really needed her mother or father to tell her and her siblings that even though Jeffrey died, they were still happy the girls were there ... a tall task for grieving parents in their late 20s, she realizes.

Cindy also lifts the lid on her conversations about deaths with her kids ... telling Kelly both Kaia and Presley Gerber have already lost friends despite their young ages -- and, she’s tried to talk them through what to say to someone struggling with loss.

BTW ... Crawford’s talked about Jeffrey in the past too, telling stories about his battle with the disease to Oprah almost a decade ago.

As far as we can tell, this is the first she’s mentioned survivor’s guilt ... a difficult conversation to have -- no doubt the point ‘cause Crawford says she thinks people need to have more open convos about death.