My children father, is file legally separation , and I want to protect my self. I'm not working at the moment,. I want full custody of my kids

Your question is not clear. If one party has filed for "legal separation" (in Nevada, it's actually called "separate maintenance) the other can counter-claim for divorce.  And all issues are on the table -- child custody, support, alimony, and proeprty division.  For the rules governing all those subjects see the individual pages we have explaining each subject, which you can reach here.