'Eating babies' is a standard accusation in Western civilisation against one's religious or political opponents. It is the ultimate taboo, as you will realise. Hence the Romans accused the early Christians of eating babies, the medieval West accused Jews and heretics of eating babies, in medieval literature pagans eat babies, the Revolutionary French peasantry accused the French nobility of eating babies. The crusaders did eat their horses (which in Britain at least is only one step up from eating babies) and during the first crusade one group of warriors (the 'Tafurs') were accused of eating babies.
On the Tafurs, John France writes in Victory in the East: a Military History of the First Crusade (Cambridge University Press, 1994) (pp. 286-7): 'a hard-core of poor men organised under their own leaders, whose name may be derived from the big light wooden shield which many of them carried, the talevart or talevas. These desperadoes seem to have been pre-eminently North French and Fleming in origin and to have represented a quasi-autonomous force within the army.' (Note 57): 'The origin of the name is suggested by L. A. M. Sumberg, 'The Tafurs and the First Crusade', Medieval Studies, 21 (1959), 227-8; on the Tafurs see La Chanson d'Antioche, ed Suzanne Duparc-Quioc, 2 vols (Paris, 1977-8), 1 lines 2987, 4042, 4049, 4066, 4087, 4100, 4106, 4115, 4118, 4299, 4318, 6395, 6398, 6417, 8251, 8921; Guibert of Nogent says that their lord was a Norman knight who had lost his horse.'
The Tafurs were recorded to have resorted to cannibalism at the siege of Ma'arra; this was reported by Raymond of Aguilers, but not by other chroniclers of the First Crusade (France, Victory, p. 315 and note 49). It is tempting to deduce that they were accused of this crime because they were poor warriors, even peasants, despised and feared by the more noble warriors who regarded them of being capable of any depravity. In other words, the accusation reflects fear and distrust between classes, rather than what actually happened. The Christian peasantry were regarded as 'other' and 'alien' by the Christian nobles. In contrast, the Muslim warriors were brave and had their own code of warrior ethics which was very like the Christian warriors' code of ethics. But peasants did not share any warrior-ethic; they fought dirty. Hence Christian nobles could regard Christian peasants as being far more alien than Muslim warriors. They were sure that warriors would always act honourably, but they were sure that they could never trust the peasants to behave honourably!
Alternatively, it is possible that the story of cannibalism originated with the Tafurs themselves. If they put it about that they ate the bodies of their dead enemies after battle they would scare their enemies so much that any enemy they met would flee rather than fight them.
Even thought they were so feared even by their own side, the Tafurs went on to become popular characters in the epic poems about of the First Crusade. In later reworkings of the epic they became little more than lovable barbarians, who ate their enemies after defeating them.
In Western Europe it was more usually the religious enemy who was accused of baby-eating - the people the crusaders fight, not the crusaders themselves. A good example is a scene in one of the King Arthur stories, The Alliterative Morte Arthure, lines 1065-6. This poem was written in England in the late fourteenth or early fifteenth century. It is, of course, fiction, but it gives us an idea of contemporary attitudes and ideals. The episode in question occurs when King Arthur goes to fight a pagan giant on Mont St Michel in Brittany. The giant hates all Christians and has been ravaging the countryside and carrying off women and children. Arthur has told his men that he is 'going on pilgrimage' (another word for a crusade) and the author tells us that all Arthur's armour comes from the Holy Land, so that all-in-all Arthur's battle is set out as the equivalent of a crusade. When Arthur finds the giant, the giant is roasting Christian babies on a spit. Arthur challenges the giant and, with God's aid, kills him, thus avenging the women and children and stopping the giant's tyranny. Arthur's victory over this symbol of evil shows that Arthur is God's representative on Earth. Possibly Arthur is intended to represent the English monarch, or to be an example to him.