What should cats eat and how many times a day?

Cats are nibblers. I have two full grown cats that I put their cat food out in a bowl of the mornings and they pick at it all day long. I fed them the same way when they were kittens but they had smaller bowls then. The bowl they have now holds about about 2 cups of dry cat food. They occasinaly get a treat of canned cat food about once a week. When they were kittens I fed them the same way but only about 1 cup a day. My cats eat periodically throughout the day and it averages out to about 4 times.