I feel like an idiot for not knowing about this until now. Now, I am intensely interested and would like to know if any of you know of any ballads about it. Here is some info I found in a Medieval Sourcebook online:

Medieval Sourcebook:
Chronica Regiae Coloniensis, s.a.1213
The "Children's Crusade", 1212

[Adapted from Brundage] Never in the thirteenth century was there to be a general coalition of Western kings for a Crusade, as there had been in 1187. This was in part due, no doubt, to the internal politics of thirteenth century Europe, in part to the gradual decline of the Crusading movement itself. That the spirit of the Crusade was not dead is amply proved by the eight large expeditions from various quarters of Europe during the thirteenth century. The survival of the Crusading spirit during the century is further shown by the extraordinary movement in 1212 which is known as the Children's Crusade. This expedition which, of course, was not a Crusade at all in the strict sense of the term ­ attracted thousands of children and young adults from northern France and western Germany to its banners.

The "Crusade" was preached in France by a peasant boy named Stephen from a village near Vendome. In Germany, a boy named Nicholas from Cologne started the movement . The sorry business was summarized by a chronicler in these terms:

"In this year occurred an outstanding thing and one much to be marveled at, for it is unheard of throughout the ages. About the time of Easter and Pentecost,4 without anyone having preached or called for it and prompted by I know not what spirit, many thousands of boys, ranging in age from six years to full maturity, left the plows or carts which they were driving, the flocks which they were pasturing, and anything else which they were doing. This they did despite the wishes of their parents, relatives, and friends who sought to make them draw back. Suddenly one ran after another to take the cross. Thus, by groups of twenty, or fifty, or a hundred, they put up banners and began to journey to Jerusalem. They were asked by many people on whose advice or at whose urging they had set out upon this path. They were asked especially since only a few years ago many kings, a great many dukes, and innumerable people in powerful companies had gone there and had returned with the business unfinished. The present groups, morever, were stfll of tender years and were neither strong enough nor powerful enough to do anything. Everyone, therefore, accounted them foolish and imprudent for trying to do this. They briefly replied that they were equal to the Divine will in this matter and that, whatever God might wish to do with them, they would accept it willingly and with humble spirit. They thus made some little progress on their journey. Some were turned back at Metz, others at Piacenza, and others even at Rome. Still others got to Marseilles, but whether they crossed to the Holy Land or what their end was is uncertain. One thing is sure: that of the many thousands who rose up, only very few returned."

Source:

Chronica Regiae Coloniensis Continuatio prima, s.a.1213, MGH SS XXIV 17-18, translated by James Brundage, The Crusades: A Documentary History, (Milwaukee, WI: Marquette University Press, 1962), 213 Copyright note: Professor Brundage informed the Medieval Sourcebook that copyright was not renewed on this work. Moreover he gave permission for use of his translations.