MARACAIBO, Venezuela — In their final minutes together, Jean Carlos, 8, held his mother’s hand like an anchor and promised to “take deep breaths” so he wouldn’t cry. His sister, Crisol, 10, hid angrily in the kitchen. His brother, Cristian, 12, hauled a blue suitcase into the yard.

Past the family gate, Aura Fernández, 38, a single mother of 10, beat back a surge of tears. Her bus came rolling down the road. Then she kissed her children, climbed aboard and disappeared.

“I love you,” she said just before setting out. “Study hard.”

Seven years into an economic collapse, Venezuela’s migrant crisis has grown into one of the largest in the world. Millions have already left. By the end of 2020, an estimated 6.5 million people will have fled, according to the United Nations refugee agency — a number rarely, if ever, seen outside of war.

But hidden inside that data is a startling phenomenon. Venezuela’s mothers and fathers, determined to find work, food and medicine, are leaving hundreds of thousands of children in the care of grandparents, aunts, uncles and even siblings who have barely passed puberty themselves.