ITIN ?

I have been in USA for almost five years. My hu*****and is in China.My son lives with me this year. He is 7 years old. Do I need apply for a ITIN for him for tax return? What documents are needed to apply for a ITIN?

by the way, when I filled W4 form, I was identified as single. Is it correct? How do I changed it? I am working at a university.

many thanks to you!