In worlds with magic or superpowers, can't you have them aid in child rearing?
Time manipulation to either stall or speedrun the pregnancy, governmental or charitable daycares that use superpowers or magic to effectively care for your kids while their parents do other stuff, using superpowers to generate resources like food/materials/money/space/time...
For a bonus, the caretaker could be another option for a lady to knock up! Hell, one of your harem members could be dedicated to doing it while the others stick to their niches.
Any of these sound appealing?