Is a high calorie, high fat or high protein diet beneficial to young cystic fibrosis patients?

Not high fat: One of the problems folks with CF have is that their pancreatic duct gets blocked. This means that the fat-digesting enzymes from their pancreas can't get to their gut and break down the fat they eat. A high-fat diet would be very bad in this situation. You need to have conversations with your CF doc to optimize your diet. You should have both a pulmonologist and a GI doc on your team.

Yes: In general, CF kids need much more fat and salt in their diet since their generic defect prevents proper management of sodium.