They represent a big challenge to the Biden administration as it grapples with the ongoing issues on the nation's southern border: unaccompanied minors -- children and adolescents who come to the United States alone or without any immediate family member. 

Some arrive with a name they have memorized, a phone number written down on a piece of paper, or a U.S. state they know by heart: the place where their father or mother now lives. 

What many do not have is a physical memory of that parent, who left when they were young or before they were born.

The migration of these minors -- some as young as 5 and others who are in their teens -- is the cause and consequence of migration itself: First their parents emigrated, and now they've come to the U.S. to reunite with their families.

There are currently almost 16,000 minors in the custody of U.S. authorities, 4,878 in Border Patrol facilities and 10,800 more in the care of the Department of Health and Human Services, according to official data collected by NBC News. They are waiting to be released with a family member or sponsor in the United States.

We spoke to some of the children and teens, all Hondurans, after they crossed the Rio Grande and into Texas.