I think being honest with yourself - and others by extension is the key. Someone else won't MAKE you happy. And no one really knows they want to marry and have kids with someone they just met on a first date. It's so hypothetical. So be honest with yourself and that will flow into your relations with others.
When I met my wife, the very first night, we had a really open and honest conversation about where we were/what we wanted, including talking about marriage (not to each other specifically, just we were looking to settle down). It was nice to not dance around those topics as if they were taboo, or wonder if we were wasting time by not having similar objectives.
