There are godly reasons to remain single (and therefore childless). The Apostle Paul did it, and even recommended it (under certain circumstances).
But it's the exception, not the rule.
It's not even about happiness or "fulfillment" -- it's about obedience.
If one doesn't have the gift of celibacy (and most of us don't), then--to avoid fornication--he should pursue marriage. See 1 Cor. 7.
The command to 'be fruitful and multiply' doesn't mean the same thing today, given the new creation, that it meant under the Covenant of Works (which the first Adam broke and the Last Adam fulfilled). It has been modified by the Great Commission. Which is exactly why we disciple (baptise and catechize) our covenant children.