If the child is not going to be claimed as a dependent, the child should be removed from the parent's tax return. If the parent's return has not year been filed and accepted, you should be able to efile it now without a problem. The refund on the parent's return should not be delayed.
The child's return cannot be amended until the amended form 1040X becomes available on TurboTax later in February. The amended return can then be efiled. Mailed amended returns can take up to 16 weeks or longer to process. I don't know whether efiled amended returns are processed any faster or not.
