The original intent of the founders was that the parents had to be citizens to produce citizens by birth. If they were not citizens, then their children were not citizens.

Another way of explaining it is this:

If the parents are not citizens, then that means they are citizens of ANOTHER COUNTRY, and have a LOYALTY AND DUTY to that other country.

The children, then, grow up with some loyalty to that other country, too, which makes them loyal to that other country.

The original intent of the founders was that the parents had to be citizens to produce citizens by birth. If they were not citizens, then their children were not citizens.

Another way of explaining it is this:

If the parents are not citizens, then that means they are citizens of ANOTHER COUNTRY, and have a LOYALTY AND DUTY to that other country.

The children, then, grow up with some loyalty to that other country, too, which makes them citizens of that other country, too.