You can't for this tax season but you can apply for an IP PIN for next year ... https://www.irs.gov/identity-theft-fraud-scams/get-an-identity-protection-pin#:~:text=An%20Identity%20Protection%20PIN%20(IP%20PIN)%20is%20a%20six%2D,or%20Individual%20Taxpayer%20Identification%20Number.&text=Spouses%20and%20dependents%20are%20eligible,pass%20the%20identity%20verification%20process.
If someone else claims your child(ren) and files first, your e-file will be rejected. If that happens then you need to print sign and mail your own tax return that claims the children. The IRS will process your mailed return; in about a year you and the other party will receive letters and will need to show proof of who could rightfully claim the children.
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.