most secular people don't equate marriage with children at all. i come from a catholic background so it was something on my mind going in. even still, the "discussion" with my then Fiancé was basically:

"do you want kids?"

"not now, but maybe one day."

"yeah, me too."

"k"

but at that time we didn't know what we wanted, we just knew what we didn't want...

but i've known quite a few people over time that aren't in a relationship with the other person, but their idea of the other person. having those kinds of big discussions might shatter that illusion.