Some unnamed, self-proclaimed Libertarian told you. And, even though you can't find any supporting evidence in the plethora of Libertarian Party materials, you assert it as fact? Heck, I once had a christian tell me that you couldn't go to heaven unless you handled deadly snakes and spoke in tongues. Would that qualify as enough evidence to smear the entire breadth of the christian church? I think not. Furthermore, I call into question your ability to accurately represent what you claim to have been told.
As regards child support enforcement by government; It certainly would be appropriate in many circumstances, and I doubt that you'll ever find a blanket rejection of it by the Libertarian Party. That being said, today's form of government involvement in that enterprise is a corrupted mess that violates the rights of all involved in too many cases.