What can I do if my girl friend brother filled my child

[VolvoGirl]

You can mail your return and the IRS will send you both letters to determine who can claim your child.  Does your girlfriend live with her brother?  Did he claim your girlfriend too?

[xmasbaby0]

Someone else claimed my dependent and my return was rejected

If someone else claimed your dependent already, then your e-filed return will be rejected.  Print, sign and mail your own return which claims your dependent.  Mailed returns are processed differently by the IRS.  It will take some time (maybe even up to a year) but eventually the IRS will contact both parties and sort out who could rightfully claim the dependent.  The person who wrongfully claimed the dependent will face repayment of refund $, plus penalties.