If I am separated (2yrs) with 2 children and made 13,000 this year can I file head of household?

Yes, if you paid more than half the cost of the household. Your U.S. Tax Return: Filing Status: Head of Household (http://taxipay.blogspot.com/2008/05/head-of-household.html)

Note that to file as HoH you must be the custodial parent (the children must have lived with you for at least half the year). This is a different requirement than whether you can claim the children as dependents.