Why do you think someone else claimed your child? Did you get a rejection message that says her SSN has been used already? If that happened then you will need to print, sign and mail your tax return. You will not be able to e-file.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.
Federal and state returns must be in separate envelopes and they are mailed to different addresses. Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.