My three babies that are 6mths old, 2 of them weigh 6lbs. and one weighs 2lbs. They mostly eat boiled chicken and turkey meat. They free feed on Natural Balance small bits during the day, which they don't eat a lot of it. Well, they finally finished the bag of food. Should I buy something that has more protein in it, since Nat. Balance isn't high in protein so they will get the recommended amount. If so, which one do you recommend?