No you cannot claim a child who is not related to you as a qualifying child for earned income credit. If neither your girl friend or the other parent is claiming the child on a tax return, you may be able to claim the child on your tax return as a qualifying relative dependent and get the $4000 dependency exemption but no other tax benefits.
The child must meet the following requirements for you to claim the child on your tax return:
1. The person cannot be your qualifying child or the qualifying child of any other taxpayer. A child is not the qualifying child of any other taxpayer if the child's parent (or any other person for whom the child is defined as a qualifying child) is not required to file an income tax return or files an income tax return only to get a refund on income tax withheld.
2. The person either (a) must be related to you or (b) must live with you all year as a member of your household.
3. The person's gross taxable income for the year must be less than $4,000 in 2015.
4. You must provide more than half of the person's total support for the year.
5. The person must be a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico.
