You must file by mail - your return & refund should be processed.
Unfortunately, you will have to file your return by mail. Once a person's SSN (your child's in this case) is used on an e-filed return, the IRS will not allow it to be used on another e-filed return
See How do I print and mail my return in TurboTax Online? for instructions.
Later in the year, the IRS will send you and whoever else claimed the child separate letters asking for proof of who was entitled to claim your children on their tax return. They will provide instructions on what you need to send as proof.
