We kept our Cfers weight on with Ovaltine! It's fortified with vitamins, so it's better than mixing with chocolate or strawberry syrup which are pure sugar, it's not as heavy tasting as a Boost or similar drink, and it mixes easier (more completely) than Instant Breakfast mixes. And if you add an extra tablespoon to make it more chocolately, it's even better with more calories. This has worked not only when he was a toddler and being picky, but even today when he's not feeling well and doesn't want to eat. Ovaltine in whole milk. Even when he says he's full or not hungry, he says yes to a glass of Ovaltine. I think it's 240 calories in a cup of milk . . . but although that's not huge by itself, it can be when you are drinking 10 ounces with breakfast, 10 with morning snack, 10 with lunch, 10 with afternoon snack, 10 with dinner and 10 before bed! That's 1800 calories in a day before you eat! When he was little, we made sure he was carrying an Ovaltine sippy cup most of the day. And it's a simple change - no learning curve, no major changes, no adjustments, no psychology, no cajoling necessary. Just calories and "normal" taste. What child doesn't like the taste of chocolate milk! He was born at 5 pounds with a meconium ileus but he's maintained at around 75% for BMI for years now.
I have also discovered that most CFers love the taste of bacon . . . . they will eat up to a dozen crispy slices at a sitting! At the children's hospital, the CF nutritionist will tell you that more bacon is delivered to the CF floor than you can believe! Bacon with breakfast, bacon sandwiches, bacon cheeseburgers, bacon, bacon, bacon! Their little (and big) bodies are craving the fat.