OK, First my qualifications are 10 years as a professional seasonal tax preparer.
First thing is that this is the beginning of November and by your comment you are not yet legally divorced, is that correct? By law, you marital status is what it is as of 12/31/2013. If you are not legally divorced you have problems. If you lived with your spouse any time after June 30, the best you can do is MFS and suffer or grit your teeth and file jointly. If you are legally separated and no joint cohabitation after June, and/or divorced you should be able file as Head of Household (HH). HH requires you to pay at least 50% of house costs after taking out any assistance received and you house/support your children.
So it appears to me that in the old job you were probably claiming Married status and multiple exemptions (5?) so that there was minimum withholding. If you think that you will be qualified for HH status by the end of the year, make sure that is included in your W4 computations as an added exemption. Also there are spots for adding in Child and Dependent Care Expenses as well as Child Tax Credits (all of this depends upon the age of your children). I can easily seeing you claiming 9-10 exemptions if the children are under 16.
Still remember you only have 2 months of this income on your 2013 return if you just started this job. What you do now may have to be reworked at the beginning of next year depending upon circumstances. In your shoes, I would be at a tax preparer office as soon as I had my papers in order. Even if you think your kids are your tax claims as custodial, the IRS rule is first filed gets the credit and the later filer has to dispute the claim.
Hope this helps!
I will add something here, you talk about bus driver route etc., that may help but the key is what address does the school have on record? How about their pediatrician? THOSE are the key records for any dispute with the IRS but filing FIRST keeps the ex from even making that initial claim.
Next, I hear you and agree with using the Ramsey plan. However, if you are computer savvy, any one of the financial programs is a great tool to have. Many of them have decent income tax calculators as well.
Granted this is a bad year for you but once you are back on an even keel, it will get better! Hug your kids and keep the shiny side up! God Bless!