I'd be surprised if they were preying upon one of the family, not only don't they practice infanticide/siblicide/fratricide (and therefore wouldn't see a peregrine as prey) but this tend to want to catch their own food and while they may store it for short periods, they don't just leave it "out" so to speak.
Stranger things can happen I guess ... fortunately, nothing like that in the 'Peg ...