Before you have kids, I see little need to buy life insurance if both spouses already work and earn enough to support a frugal lifestyle for one person.
After you have kids, things change a bit. Single parenting with a full-time job seems like an extremely difficult thing to do, difficult enough that you may decide it's worth buying enough life insurance so that you never have to do it. To determine how much is "enough," take the following into account:
1) Your assets,
2) Any life insurance your employer already buys for you, and
3) Social Security survivor's benefits (or any equivalent foreign program that may apply to you).
The Social Security piece is a big one that I think many people overlook when buying life insurance. In my case, if I died tomorrow, each hypothetical child of mine would get about $20k/year until graduating high school, and my wife would receive the same amount until the youngest hypothetical child turned 16. These benefits are subject to a family maximum of about $45k/year, and the spousal benefit would be phased out if she continued to work and her earnings were above a certain limit. Everyone's benefit amount is different based on their work history, so you should check online for the numbers that would apply to you.
In our case, these benefits are large enough that they should be able to completely cover reasonable living expenses until the kids are grown. A true Mustachian would find a way to invest some of this money for a college fund and/or retirement. In addition, any previously owned assets, combined with any life insurance payout, would be able to compound during the time the benefits are being paid out.
I would say it's entirely possible that if you plan to have $500k plus a paid-off house when you have your first child, that plus the Social Security survivor's benefits could be enough to ensure a comfortable childhood for any children plus a comfortable retirement for the surviving spouse if one of you were to pass away.