Commonly, when people marry for a second or subsequent time, one or both spouses already has children. According to 2015 Pew Research Center report, about 16 percent of all kids live in "blended families." These are families that include a step-parent and possibly one or more step-siblings.

Discuss Your Goals

Since nearly all marriages involve the commingling of finances, it's essential for couples preparing to tie the knot to discuss their financial goals, what they want to spend money on and what they want to save for. However, when there are children involved, these discussions are even more crucial.

Likely, one spouse has more assets than the other coming into the marriage. Further, one may have more children than the other, or have kids who have special needs, talents or interests that require greater expenditures. Of course, the children's other parents will likely continue to play a role in providing some support for them as well.

What You Need to Consider

Determining which of your assets you combine and which you will keep separate once you're married is key. Will you each pay only for your own children's care or will you pay for everything out of one pool of money? This may impact the amount of child support which you or your spouse receives in the future from your ex.

A prenuptial agreement, while a good idea for virtually all couples, is particularly important for couples who are blending their families, even if all of the kids won't be living under one roof all of the time, Brady Bunch-style.

You'll want to determine who will pay for routine expenses like clothes, school, medical care and extracurricular activities. However, you also need to determine if or how you'll blend your resources to cover things like family vacations, college, cars and of course your own retirement. As with every prenuptial agreement, it's essential that both spouses-to-be disclose all of their assets and debts fully and accurately.

It's best if both partners have their own family law attorneys to help them draft the prenup or at least review it before you sign it. This will help ensure that it accomplishes what they intend for it to, that nothing is left out and that both spouses and their children are protected.