How do you know your child's best learning style?

Use a variety of different techniques and then OBSERVE.

I do not teach kids but the only way to know the style of a student is to watch them at work

Exercises and questions in a systematic manner and different in content and Observe

various methods avialable to know that,,, activities based education is the answer .

Experience and follow-up

Friendship is the answer of your question. When you come to close him, you can observe his attention to ward learning. 

THEIR SOCIAL BEHAVIOUR AND LIVING WILL CERTAINLY ENABLES US TO KNOW ABOUT THEIR LEARNING ATTITUDE