For most young parents, writing a will is less about leaving their assets than it is about naming guardians for the kids. The guardian you name in your will is the person who would take over if both you and the other parent were unavailable to raise your children. That’s very unlikely, but worth addressing just in case.
If your children ever needed a guardian, the local court would appoint the person you nominated in your will, absent a serious problem with that person. You can name different guardians for different children if you wish.
If you haven’t made your wishes clear in your will, however, the court would have to choose someone without any guidance from you. The common choice is a family member. But what if you really wouldn’t want certain family members to raise your children? Or if you would prefer that a close friend, who has a good relationship with your kids, step in as guardian? The court wouldn’t have any way of knowing.
Many, many parents get stuck when they go to choose a guardian—after all, no one likes even thinking about someone else raising their children. And parents sometimes discover that they disagree about who would be best.

1) Your First Choice Is Older Than You Are: The best solution is to forget about what might happen in 10 years, and just pick someone now who could take care of your children in the next three to five years, knowing that you can change their guardian choices as the children, and their nominated guardians, grow older.
2) Your Family Won't Like Your Choices: Your first loyalty is to your children, and you should always make the choices that you think will serve them best. You should also know that a court challenge to your choice of guardian is unlikely -- and unlikely to succeed. A family member who wanted to overturn your choice of guardian would have to prove to a judge that there was a very good reason to set your choice aside. To prevent conflict as best you can, leave a written explanation of your choices. It can calm tension, and if necessary it could be used in court.
3) You Worry That Your Children Won't Like Your Choices: So talk it over with them. If you think your children won't like your nominations for guardians, you might want to discuss it with them, especially if they're already in their teens. In Missouri, a child 11 years or older may ask the court for a different guardian than the one nominated by their parents. The judge will take their wishes into account along with other factors.
4) Your First Choice Is Not a Good Money Manager: If the person you want to raise your children is not good with finances, that is easily fixed. Just name someone else to manage your children's money, and leave the guardian with only the job of making sure your child grows up well cared for and as happy as possible.
5) You Don't Like Your First Choice's Spouse: What if only one person in a couple is your choice for guardian? Just name the person you want -- not both of them -- as guardians. That way, if the couple divorces, your kids could stay with the person you feel closest to.
6) Your First Choice Lives Far Away: There's no requirement that a guardian live where you live, but having an out-of-state guardian complicates things. A nonresident may have to post a bond (a sum of money or an insurance policy) as insurance that they will faithfully perform their duties as a guardian. Also, an out-of-state guardian would have to get the guardianship proceeding moved to the state where they live. If you want to name someone far away as a guardian, also nominate someone local who could serve as a temporary guardian. This person could take care of your children until your permanent guardians could get to them.
7) You Have Children From Previous Marriages: Blended families are common these days, making guardianship choices even more complicated. Some parents name different guardians for the children of different marriages. Others make a plan that would keep all the children together. Remember that guardianship doesn't come into play at all if a child has a surviving parent, and that's more likely when their parents are not living or traveling together.
8) You Don't Want Your Ex-Spouse to Get Custody: If you're divorced, you may not like the idea that should you die first, your ex-spouse would get custody of your children. That is what would happen, unless the parent is clearly unfit. If you really don't want your ex-spouse to take custody of your children, explain why in your will or in a letter. Include court records, police reports, or any other evidence of your ex's unsuitability as a custodial parent. Give that letter to your first choice for a guardian, to be used as evidence of your wishes in the case of a court proceeding.