As described in a previous post, children could be dedicated to the church around the same age that their peers entered school or began professional training. They were not forced to take vows when they got old enough. Monks and nuns were very aware that one of the vows was of “stability,” essentially a promise never to leave the walls of the community unless sent by the Abbot. It was not an easy vow to keep, and they had all known of novices who climbed over the wall and ran away. Much better never to vow.
So the children who grew up in monasteries were permitted to leave, if they chose. But as you might notice, they had a problem: they had missed out on years of alternative training. It might not be as much of an issue if they had been trained in a useful profession at the convent or monastery.
Monasteries always had a core population were choir monks, the most educated ones who sang and prayed, read and copied books. But monasteries also ran businesses. Generations of rich people had left farms, manors, and even mines to monasteries in their wills. Lay brothers had to manage these businesses to generate income that supported the choir monks. So perhaps some of the children raised in monasteries had learned a trade. They had certainly been taught to read, so might make a decent shift as teachers.
But in any event, it seems most of the children who grew up in monasteries took vows. It was a very bad thing to be cut loose in medieval society; you needed to have a place where you belonged: family, guild, church, lord’s service, something. These children knew the monastery and belonged there.
At the same time, there were always young men or women entering the monastic life for the first time at early adulthood. Some were girls fleeing unacceptable arranged marriages in the only permissible way. Some were knights who had sickened with killing or had other crimes on their consciences. Perhaps some others were failed university students.
Then as now, they joined as novices for a trial period. If they could, they brought property or some kind of donation. When a girl’s family wanted her to join a convent, they gave her dowry to the Order.
Why would someone join an Order instead of leading an ordinary life in the world? The men and women who joined a monastery had security that others lacked; belonging to a monastery meant health care and legal protection. While medieval people were as interested in sex as anyone else, they must have observed that family life was often tragic and discouraging. Living as a single person in a monastic community, they need never experience childbirth or the death of children. They would not have to choose which mouth to feed in a famine. They could live in an envelope of meaning, certain that their daily work was somehow redeeming the world in God’s eyes.