Having kids doesn't change the math. That's MMM's point in the post. It's all about savings rate. Kids mean it is harder to save 35%, but the math doesn't change.
I'd add that even if you aren't able to live on 35% for 10 years straight you shouldn't fall into the mindset that it's not worth aiming for at all.
Or do, and cut from other areas/don't get on the hoighty-toighty daycare/lessons/private school treadmill. But kids are definitely an expense.