Parents want to raise children with a moral sense of right and wrong and to develop a conscience. This allows children to set limits for themselves when they are on their own. Children need to learn how to think, not just what to think. If a child learns problem solving skills, when a problem does arise, with a parent's help, she can think through what needs to be done. Discipline helps children to learn to appreciate the natural results of their behaviour.
Parents intervene when safety is an issue.
If it won't harm them, parents can let their children learn by natural and logical consequences. If a toddler leaves her favourite book outdoors, it will get wet and damaged. She will have to wash them herself. Parents want children to be socially acceptable and to be good friends to others. For this reason they teach pre-schoolers to share toys and to take turns.