Does the three different types of citizen consume the same amount of food? I've read the How much food does a person need each year? answer.
Since the answer of "How much food does a person need each year?" was derived by dividing total population by food consumption, there's no reason to believe students or children consume less food. DeadMG confirmed the same number from his own calculations, and given that his ratio of adults/students/children is likely to be slightly different, it's safe to conclude each citizen eats the same amount.
The food consumption in Banished is not really important per Citizen. It is important to think per house.
Now this might seem weird at a first glance, but if you click on any house, you will see the inventory tab. That inventory gets filled by the tenants with what they need, such as food and Firewood. Now if you have, let's say a house with 8 tenants, they will fill up that inventory with food. Now if you build a second house, some of those 8 tenants move out ( a married couple for example ) and in their new house, they will start filling the inventory with food again.
So while you might stay on the number of Citizens, you will need more food if you build a new house, due to the inventory system. So it is actually more important to beef up food production if you build houses, than if you gain a few new adults/students/children.