"¿Cuántos hijos tiene ella?"
Translation:How many children does she have?
Subjects typically go after the verb in Spanish questions: http://spanish.about.com/od/sentencestructure/a/sentenceorder.htm
@dkat - re: ...stress when it would stressed naturally?
Hola dkat. You noticed something very important. The Spanish language has accent marks that serve different purposes. In the case of the accent marks that you noticed, they fall on the part of the word that is naturally stressed. So they can't change anything regarding the pronunciation. So why are they there?
In this case, the accent marks are called orthographic accents. Check out this hyperlink.
If we add the sentence structure, "How many sons (children) does she have?" to this list, does any one of them break an English grammar rule.
What sounds correct to one person is subjective and varies from place to place in the larger English speaking world.
It's best to base the correctness of sentence construction on rules of grammar which are objective.
Hijos can refer to only the male offspring of a particular person or the combination of male and female offspring of a particular person. There is a lot of information in the word hijos.
Niños refers to male children in general or male and female children in general. We don't get the extra piece of information about the parent.