For purposes of this answer I am assuming you file as head of household and that your children are under age 13.
Accordingly, you may be eligible for a Federal refund of as much as $4,250 comprised of the refundable child tax credit (about $1,900) and the earned income tax credit (about $2,350).
Child Tax Credit
Ordinarily the $1,000 child tax credit is non-refundable to the extent you have a tax liability. However, your Federal tax liability after considering the child care credit will be slightly above $100. This means the bulk of your child care credit may be refunded to you.
Earned Income Tax Credit
You appear to be eligible to claim the earned income tax credit which is a refundable credit. Below are the rules for claiming this credit.
Generally to claim the earned income tax credit you must file a U.S. tax return, must be a citizen, you must have earned income, you must have a valid Social Security Number for yourself, your spouse (if filing jointly) and your qualifying child, your investment income is limited to $2,650, your filing status cannot be “married filing separately” and you cannot be a qualifying child/dependent of another person. The maximum credit for 2005 for a qualifying person with two qualifying children was $4,400 ($2,662 with one qualifying child, $399 with no qualifying children).
Earned income and adjusted gross income (AGI) must each be less than:
A qualifying child is one who is (1) your child or stepchild (whether by blood or adoption), foster child, sibling or stepsibling, or a descendant of one of these; (2) has the same principal residence as the taxpayer for more than half the tax year (some exceptions exist for divorces, deaths, etc.); (3) the child must be under the age of 19 at the end of the tax year, or under the age of 24 if a full-time student for at least five months of the year, or be permanently and totally disabled at any time during the year; and (4) the child did not provide more than one-half of his/her own support for the year.
To claim the credit you need to complete and file Schedule EIC with your tax return (see http://www.irs.gov/pub/irs-pdf/f1040sei.pdf). You might also want to visit the following website to get more information about the earned income tax credit. http://www.irs.gov/irs/article/0,,id=134524,00.html.
You may qualify for the "advance earned income credit" which will allow you to collect part of your credit in advance from your employer through an addition in your wages. If you have at least one qualifying child fill out form W-5 and give it to your employer (see http://www.irs.gov/pub/irs-pdf/fw5_04.pdf).
If you are not familiar with these provisions I recommend you engage a qualified tax preparer who can walk you through these credits and get you the most refund.
Because it is impossible for me to identify and consider ALL the relevant facts, this advice is not intended or written to be used for the purpose of avoiding penalties, and cannot be used for that purpose.