Ohserendipity

Planning on taking my grandson who is 13 on a cruise with me. He does not have a passport and that presently is not an option. How will this work? What do I need? Does any of that change if his father goes with us? I am just worried that we will be denied boarding if it is just him and I - honestly still concerned about it if his father goes as his mother is not and we will not have a passport for him.