Why would a divorced parent suddenly need a childs SSN?

It was an amicable split about two years ago now.

Child lives with parent A about 60% of the time. Parent A maintains a home, provides for the childs general welfare including the majority of the clothing, health insurance and treatment if necessary, arranges school, etc. Parent B has the child a couple of times a week. Parent B floated from friend to friend until last May when he rented an apartment close by, in the same school district. Parent B has the child two to three days a week, no set schedule but many times every other day. Both parents have, and live with, significant others.

Parent B suddenly requests the childs SSN number. When asked why says that his lease is up and he is renting a single-family home and needs it for that.

Does that sound right? I have been in the rental business for several years now and have never asked for a childs SSN for a lease. We have a blank where children, and others who may be living there, are listed and we do ask for SSN’s on all adults but we also do background checks on all tenants.

One final item, last week Parent A jumped on Parent B’s butt because the school called Parent A to complain about the number of tardies and absences. Turns out of the 40 school days Parent B had the child, she had been late 28 times and absent three. Parent B was told by Parent A that if he could not be more responsible and if there were any more tardies or unknown/unexcused absences that Parent A would take full custody of the child from Sunday evening to Friday afternoon. She would not cut off all contact, Parent B could still pick the child up and interact with her in the afternoon but that child would need to be at her home from 7pm in the evening in order to do homework and still get to bed at a decent hour.

I apologize for the long ramble.

What could be the real reason this is suddenly become important to Parent B? Is he planning some kind of legal action?

What are all the possible reasons that a childs SSN would be needed or necessary?

Hive minds are better than one. What am I missing; thought and ideas all?