Say you pass away in a car accident, along with your spouse. That's why you're doing your estate planning after all -- to make sure you're ready for the unexpected.
If you have minor children, what happens to them in this situation? You can't care for them any longer, so you need to have that plan in place well in advance.
If you do not have a plan, the police may simply pick them up and then contact Child Protective Services (CPS). They could wind up with CPS for a short time or for a while, depending on the complexity of the case. They may even end up in foster care. Eventually, the court can decide who is legally allowed to care for them, likely giving them to a family member, but how long is that going to take?
To help your children avoid this process, you want to pick "first responders." These are people you name who can have the children immediately if you pass away or get seriously injured. Officially selecting them gives them proper documentation. They can easily prove to the authorities that the children should be released into their custody right away.
These first responders may also be the people you choose to be their long-term guardians, or they may not. It all depends on what you want to do. But the key is to think of making the process easier for the children, and that means ensuring that things go as smoothly as possible, considering the circumstances.
At every step in this estate planning process, make sure you know exactly how to proceed.