Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed. So then, the law was our guardian until Christ came, in order that we might be justified by faith. But now that faith has come, we are no longer under a guardian, for in Christ Jesus you are all sons of God, through faith. (Galatians 3:23-26, ESV)
The slave assigned to this role would watch out for the student on his
way to school and help him with his manners and schoolwork, but he
was not the teacher himself. Children sometimes resented but often
grew fond of their slave guardians and later freed them.
[Keener, C. S. (1993). The IVP Bible background commentary : New Testament (Ga 3:24). Downers Grove, Ill.: InterVarsity Press.]
While Paul in Galatians 3:23-26 explains the relationship of the law to grace, his illustration confirms children need more supervision and less responsibility than adults. Parents need to make important decisions for children until they demonstrate the ability to make responsible decisions.
Paul's analogy confirms the goal of parents is to raise their children to become responsible adults living under grace rather than irresponsible adults who need governmental supervision through garnished wages, imposed fines, imprisonment, or probation.
Just as a baby bird needs the security of the nest, children need the security of parental guidance. The parent birds' goal is for the baby bird to learn to fly. But, it would be cruel to push baby birds out of the nest before they're ready. In the same way, parents need to teach their children to make responsible choices while under the safety net of parental authority and discipline.
The irony is many educators shun corporal punishment under the guise that it damages the child's pyche (the Greek word for soul). The same thinking pushes children to have more adult rights than they can handle. This combination is cruel when it compensates for children's ineffective discipline with criminal charges, especially when school administrators equate zero tolerance with zero judgment and punish trivial misbehavior with their most severe punishment.
Children need their parents to guide them, teach them (Deuteronomy 6:6-7), and discipline them (Hebrews 12:5-11) with firm loving discipline, not indifferent punishment that gives them the same responsibility as adults and treats them as criminals.
Just as some in our society push children into adulthood, others assert grace without the preexistence of law. They want grace as an indulgence, tearing down the standards, rather than grace renewing the heart to desire and live by God's standards. That's why the law came (Galatians 3:19) before Christ.