Children THRIVE on routine.
Think about this. A child is basically powerless about how his day will go each day. He is totally dependent on the whims and opinions of others whether or not (and when) each thing happens daily.
So if sometimes he get's lunch when he's hungry, but many times he doesn't, he's going to feel pretty insecure about getting his hunger taken care of. And he's going to be whiny. He's going to bug you until it drives you crazy about what he's going to have for lunch and when it's going to be.
Routines give children security because they can count on what to expect each day. As children get older, they can handle more disruption from routine. They "get" that even if lunch is late, it will still come. So the younger the child, the more routine they need.
I learned how well children thrive on routine when I took in a foster child for a while. Someone told me to make a chart, so the child would know what to expect, and not feel so lost in a new home. I thought that sounded like a good idea, so I made up a chart of the daily routine, rules, and a list of what kind of behavior was expected in the home. The foster child LOVED it! But my own children loved it even more. They went crazy over it. I was shocked because I thought they didn't care about routine. Apparently I was wrong. And ever since then, I've relied on routines to help my children feel more secure and well cared for.
I have to tell you...it works. They are way less whiny. And much happier. What kind of routines have worked for you in your family?