um... show them the receipts from you paying your taxes ( you can even get them printed out again down at the tax office ) then simply make copies of your kids birth certificates (or you can order new copies from the state) and your done.
I am not sure what the big deal here is.
the big deal is my daughter goes to public school and i pay my local real estate and school taxes- they have the records on file yet i have to prove all of this???
if i didn’t pay my school/property taxes what do you think would happen???