You have 2 options.

Have the taxpayer on the parents return apply for an IPPIN.  Once you have that, their return will be accepted with the child on it.

OR

Paper file, be sure to include the 8948 with the rejection message..

You're wasting time trying to call anyone about this, you wont get any information.

The taxpayer went through the long process and got a PIN and has since had his tax return accepted.