One of my colleagues was asked during a recent presentation about when she should stop helping her son wipe himself after using the bathroom. When she asked the child's age, she learned he's 10-years-old! The mom was concerned he'd get a rash if she didn't help him. While this might happen, he'd quickly learn from the consequences.
Sometime before your children are 5 or 6-years-old, you should be completely be out of their bathroom business. It's important for your children to take control over their own bodies. It can help kids to start with toilet paper and finish off with a flushable wipe. They'll learn to do a good job after enough practice!