I know of one guy that did this a couple of years ago.
The financial side was the same as marriage. (although the law actually states that no seasoning is needed, so might want to check that).
The documents were: Copy of childs ID card (if over 7). A copy and original of birth certificate. The copies of court papers. Proof that you live together and take care of your child. Not listed but worth taking would be copies of ID and house reg of the mother of the child. Also you need to take your child to immigration with you.