Wait----were you talking about your spouse's SSN or the SSN of a child? If you are filing married filing separately, you are supposed to enter your spouse's SSN.
If I am filing a separate return why do I have to list my spouse’s information on my return?
Even if you file separate returns (the worst way to file) you each have to list each other's SSN's and some other information on your own tax return. The IRS can then cross check to make sure you are not "double dipping" for itemized deductions, dependents, etc.
If you are in a community property state, there is more information that will be needed.
Community property states: AZ, CA, ID, LA, NV, NM, TX, WA, WI
https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states
https://turbotax.intuit.com/tax-tips/marriage/five-tax-tips-for-community-property-states/L4jG7cq7Z
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
