Swedes are less inclined to marry in the traditional sense but more inclined to long-term shack-up arrangements (or common law marriages). If people live together for life without officially marrying and raise children that way, then it would be hard for me to deny it's a viable family.
Shacking up for a few months before deciding to get married would make marriages and families stronger, too. People don't appreciate what a pain in the ass living with someone can be.