Kitten food is usually higher protein/fat. We don't have the budget for high quality kibble and we can't feed wet food all the time at the shelter I volunteer at so I usually try to feed kitten food to the cats that need to gain weight. It helps some.
Fancy Feast Kitten wet food is actually one of my favorites to feed them. Iams Kitten and Purina One Kitten dry food are also fairly good. I wouldn't feed either of these to my own cat though.