CGP

Aside everything that’s already been said, this may come off a bit drastic, but until the N400 is adjudicated and put to bed, I wouldn’t travel out of the country unless it becomes very necessary. Your N400 conundrum seems to have several moving parts and the last thing you want is to travel outside and then try to re-enter to face a probable secondary inspection(SI) at the POE. It might not be anything, but the mere mention of SI, the wait and its attendant possible “interrogation “ could get messy and put your BP through the roof. 

Aside everything that’s already been said, this may come off a bit drastic, but until the N400 is adjudicated and put to bed, I wouldn’t travel out of the country unless it becomes very necessary. Your N400 conundrum seems to have several moving parts and the last thing you want is to travel outside and then try to re-enter to face a probable secondary inspection(SI) at the POE. It might not be anything, but the mere mention of SI, the wait and its attendant possible “interrogation “ could get messy and put your BP through the roof. 

I know its 'child support', but in your case the prevailing circumstances might make it difficult to produce any tangible documents as proof of ' child support'.
Now what I'm thinking is if you have your child as the beneficiary of any insurance plan or as dependent on you tax records you could probably upload those documents.
At the interview I'm sure you can expalin your way out with the officer.

It is not a mandatory request to all married applicants. Applicants with a child( children) are asked to submit proof of same. i.e birth cert, etc. I would understand that applicants who don't share the same address(residence) as their child might be requested to show proof of child support.
In your case, I would just advice you to submit something (insurance docs, tax transcrpits showing child as dependent, etc etc) than ignoring the request altogether.

I know its 'child support', but in your case the prevailing circumstances might make it difficult to produce any tangible documents as proof of ' child support'.
Now what I'm thinking is if you have your child as the beneficiary of any insurance plan or as dependent on you tax records you could probably upload those documents.
At the interview I'm sure you can expalin your way out with the officer.