With little kids, it’s really just a matter of exposing them to all sorts of learning styles and seeing what works best for the kids. As they get older, you can have them take a written test that helps you to narrow down the choices.
Obviously, these tests aren’t perfect and they won’t necessarily say that a child is definitely a spatial learner or definitely a kinesthetic one. But the tests will help to narrow down the scope. You can find tests at sites like this: http://www.engr.ncsu.edu/learningstyles/ilsweb.html
Knowing what type of learner a child is helps for a number of reasons. It helps the teacher to plan her lessons and to think about the learning styles to try to incorporate into the lesson plan. It also helps each student to know for himself what type of learner he is and to try to learn to his strengths.
A child that knows he is a visual learner should make sure that he looks at the pictures in his textbook. He should pay attention to the maps and diagrams that are provided during a lecture and should ask, when possible, to turn in assignments that include drawings, diagrams and such on them.
All of these ideas are meant to help the teacher and the learner to best use the 7 learning styles to their benefit.