A tax return listing a child in the process of being adopted must contain a valid Adoption Taxpayer Identification Number (ATIN) in order to be filed. You have the following options if you have not yet received the ATIN for your child:
File an extension on Form 4868 and wait until you receive the ATIN to file the return (generally, extensions are only granted for up to 6 months from the original filing due date).
Alternatively, you can remove the child from the return, electronically file now and receive your refund and then later file an amended return once you receive the Adoption Taxpayer Identification Number to receive the remaining refund amount.