If the father is not on the birth cert he'd have to prove that he WAS the father then, before he'd have any say in that child's future.
If the birth cert says 'father unknown', well that should may make it easier for you to bring that child here, because in theory he'll have no say in the matter anyway, but of course the mother having 'sole responsibility' will be the main issue.
I brought my 2 Filipino stepchildren here, but they both had 'father unknown' on their birth certs, and it was probably a bit easier then anyway.
Good luck, but the sooner the better.
