OCI originals submitted

[goingbrit]

Hello,
I am applying for OCI for my two children, and have two questions:
1) what originals does VFS take (and then return after a couple of days)? I'm assuming that they won't take the kids passports or the parents' ones (proof of Indian descent). Then is it the birth certificate? Naturalisation certificate?
2) should we sign the declaration at the end of the form? W have already signed the last bit for minors only, but this is the one above it that an adult applicant would normally sign.
Thanks very much,
GB