7 week old kitten is so boney yet I feed him twice a day a mixture of kitten chow, and Taste of the Wild.?

The Taste of the Wild is both wet and dry. I've had him for about a week since his mother abandoned him. I haven't got him into a vet yet because of money hardship right now but my moms working on getting the money. How can I fatten him up? His ribs, hip bones, and spine can be felt, and counted yet he has a rounded stomach.