Most kids love the sugar-filled, barely nutritious cereals that are out on the market.  Ideally, cereal for kids should be very low in sugar and high in fiber and protein, but I don’t know many kids who will eat that kind of cereal.  So maybe a sugar/fiber ratio would help.   If the cereal has a lot of sugar in it then a requirement would be that it has to have a lot of fiber.  For example, Cinnamon Spoon Size Shredded Wheat has 12g of sugar & 6g of fiber (& 4g of protein) which is a really good amount of fiber.  If the cereal has a moderate amount of sugar then it would need to have a moderate amount of fiber.  Wheaties has a really good ratio with 4g of sugar and 3g of fiber.   Cheerios only have 1g of sugar and yet have 3g of fiber (& 3g of protein), so Cheerios are really great.  They probably have the best sugar/fiber ratio of all.