What medieval event in 1212 is often called the “Children’s Crusade”?

The story behind the answer

It wasn’t an official crusade or a royal levy. In 1212, waves of mostly poor adolescents and devout commoners, inspired by charismatic youths like Stephen of Cloyes in France and Nicholas of Cologne in Germany, set out toward the Mediterranean, believing faith alone would open the sea or bring a peaceful conversion of Muslims. Lacking papal sanction, military organization, or logistics, most never reached the Holy Land; many turned back, perished, or were exploited and even sold into slavery.

Later chroniclers embellished the story, popularizing the misnomer “Children’s Crusade.” Modern historians see it as a burst of lay religious enthusiasm and social distress in the wake of crusading failures after 1204, revealing how crusading ideals permeated medieval society far beyond knights and kings.