I think couples with children who want to marry "someday" should just do it. I think "marry your baby daddy days" are a wonderful idea.
The Parkcrest Christian Church in Long Beach, CA offered to the several cohabiting parents in the congregation that the church would give them a free wedding. Four couples took them up on it in a joint ceremony.
The advantage that Parkcrest had in promoting these marriages is that the couples were already part of the church. If a couple are that far along - cohabiting, with children, attending church - all they need is a little nudge.
I believe that church and state could work together on promoting "marriage now" for cohabiting parents.