With the problems facing couples in today this would help prevent any worrys and help tie together the family unit with everyone knowing the truth.
With statistics as high as 1 in 20 fathers not being the biological father of their child and the implimentation of a DNA database I think it's time we began DNA testing all fathers. This will help prevent storys such as
http://www.bbc.co.uk/news/uk-england-manchester-10845112
The law would help protect mothers, fathers and children and in most cases cement the bond between father and child and in 5% of cases allow the parner to choose or not to choose to undertake the task of raising a child that is not biologicly his own.