For the purposes of qualifying for EITC, a child is your foster child if the child is placed with you by an authorized placement agency or by judgment, decree, or other order of any court of competent jurisdiction.
In order for TurboTax to calculate the credit correctly, the question Is (your dependent) placed with you by an authorized placement agency, a judgment or court order? must be checked yes. If your foster child is your qualifying dependent and was placed in your care by an authorized placement agency, go back through TurboTax and make sure the question is answered correctly.
There are other stipulations to the EITC that may determine whether you qualify or not for the EITC. See link below that explains the qualification of EITC: