Donald Varner comment
"In FTM 2012 how do you source a parent <> child relationship? I have birth facts supported by birth certificates for an individual but I see no way of showing how I proven a specific parent / child relationship"
How about just creating [some]custom facts to handle this/these situations
You can create custom facts with such tiles as
Mother of child
Father of Child
Child of Father
Child of mother
Daughter of Mother
Son of Mother
Then you would just document them the same as you do for any other record/source
"The birth birth certificate of Jane Smith shows that Jane Smith is the daughter of John Smith"
This comes in handy when dcumenting census rcords, because a lot of them show that person X is the son/daughter of Person Y