Relax bro and be careful who you start getting mouthy with around here. First off, give better information in your initial post. If you want advice give a detailed backround regarding pertinant health issues and stats. Then tell us what the kid is currently doing to try to gain weight. Do this and you won't get called out as a bullshitter. My initial question would be why are the paerents coming to you for advice when they are obviously dealing with a pretty progressive doctor? My second question would be why are they not dealing with a dietician if the kid is that underwight? He needs calories, plain and simple. First choice would be whole and unprocessed foods but if he just won't eat I would find a meal replacement that is higher in carbs and lower in protein that he likes the taste of. Once he begins to gain weight he'll be more receptive to eating actual food and he'll begin to gain some confidence. I would try to get the kid to eat good grainy bread, peanut butter, burgers, whole milk, pancakes etc - forget the typical BBer diet of eggwhites, chicken breast and tuna, he needs calories plain and simple. Keep his sugars low if possible, he'll get plenty in the milk but up his fats and carbs especially.