Who will get my kids if I die?

My husband and I are divorced. I have custody of the kids by way of an agreement not a court order. My husband is currently in the military serving overseas. Who will get my kids if I die? Can I use a will to make this decision or does NC law automatically give custody to the biological father?

When one parent dies the children will be placed in the custody of the other parent, unless that parent is proven to be unfit and unable to care for the children.