I have raised my boyfriends children since they were babies when their "Egg Donor" walked out on them. I have paid over 90% of the kids expenses due to their father losing his job early last year. I can legally claim them as dependents under the "non-relative dependent" status, but I don't get to claim the EIC or the child tax credit without them being "blood" relatives. It's a substantial difference between the return I would get if I could claim those credits and not. Would I automatically get audited if I claimed I was the children's aunt, instead of UN-related. There is nobody else that would claim them, and I pay all my taxes like a good citizen. Please help as I hate to do something illegal, yet it's so unfair that the $8,000 I paid in childcare this year is just "Gone" (the credit I get for that is only $673!), only because I didn't give birth to them. Yet if I were the blood relative, I could get all these extra credits!

Yes, IRS computers automatically check these things. You are not eligible for Earned Income Credit or Child Tax Credit.
Also if the children are qualifying children of your b/f, you can not claim them. It is not required that b/f paid more than half of the support.
Read: Your U.S. Tax Return: Requirements for claiming a dependent (http://taxipay.blogspot.com/2008/03/requirements-for-claiming-dependent.html)

What MukatA says is completely true. It's too late for 2008 to claim either the Child Tax Credit or the Earned Income Credit, UNLESS your state recognizes your co-habitation situation as a common-law marriage. You need to check that out with your local court house.

But I have a simple solution to claim these credits for 2009: Marry the kids' father!