It's hard to have an accurate number, because not all of these parents come forward and apply for proof of citizenship for their child, but on an annual basis we may do 40,000 or more requests for a proof of citizenship for people who are born abroad. In some cases those are replacement proofs, so that number is not exact, but it gives you an idea of the number we're talking about.
On December 13th, 2010. See this statement in context.