Working parents of young children face a disappointing calculus. When they look at the paycheck of the lower-earning spouse -- still usually the wife's -- they don't see much bottom line income.

The taxes on that second income are paid at the couple's top marginal rate. A family in the middling 28 percent marginal tax bracket could see the second earner's salary cut by 43 percent or more, once state, Social Security and Medicare taxes are included.

It's no wonder that a random bad day will trigger the quit response in struggling parents: "I'm bringing home $200 a week for this?"

But there are long-term costs to not working that everyone should consider before leaving their job. Even spouses who do quit can protect themselves from some of those risks. Here are some pointers.

Bad things still happento good people. Call them the four D's -- death, divorce, disability and downturns in investment portfolios. You can add job loss by the one spouse who is working. When any of them hit, the women who fare best are those who have invested in their own education and careers, finds a study published in October 2013 by the Journal of Financial Planning.

Of course, parents should have adequate life and disability insurance whether they are working or not; nonworking spouses will have to shell out money for this coverage, just as they do when they are working.

Furthermore, families with nonworking parents will have to keep more money set aside in a general emergency fund for any of those eventualities. That may even require them to limit the amount they put into higher-yielding retirement accounts or 529 college savings plans so they can build up their emergency funds.

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Kids grow up. Even the most devoted carpool driver will have time to fill when the kids get their driver's licenses and start to break free.

If you're already in the workforce, you can ramp up your career then. But if you've not been working at all, getting back in can be a struggle. Re-entering at the level where you might have been had you worked all the way through is near impossible.

You'll have to be "selfish" either way. Some career-oriented mothers feel guilty when they look forward to the office every day, even if they are earning money that advances their whole family.

Guess what? Guilt is a mother's lot in life, and you'll probably feel badly about something else if you stay home. You will still need to put yourself first, sometime.

For example, even if you don't earn money, you'll need to spend it on yourself. A nonworking spouse should have access to money for gifts and incidentals, career-aiding activities and other items. He or she should be covered under a family health care plan, and have an individual retirement account, called a Spousal IRA.

Having your own IRA and health coverage even if you're not working isn't selfish -- it's common sense. After all, you'd look after your baby-sitter, wouldn't you?