Hello Ross,
Kids from my ex-Fil. partner.Since he had his acknowledgement on my kids birth certificate,I supplied their visa application with his letter of consent.
As long as you have proof that you have the sole custody of your child,you'll be fine.
We applied March 5,'09 and granted May 13,'09.We were lucky enough we didn't wait that long.
Anyway,from where are you?Hope you'll update us of your application.
Good luck and God bless.
Ana