I don't have an answer for it because I think giving time off to new parents are super important, but in the name of fairness, maybe X months per Y years "paid leave time" should be universally granted to all employees?
Think of it as a way to preserve the species. Or as a deep training session.
And to expand on also hinted growth of skills. Having kids - gives one abundance of opportunity to practice growing others.
Obviously you won't be around your kids all the time, nor be there for them forever. So after initial "micromanagement" phase with babies. With toddlers and older you start switching towards mentoring and coaching.
Which overlaps (not specific things, but concepts) with managers/leaders growing employees.
How would you know?