Children as old as five are going to school in nappies because they haven't been toilet trained.
Parents are failing to pass on basic skills to their children, such as recognising when they have a full bladder.
The consequence is that teachers are increasingly helping youngsters who have had 'accidents' instead of teaching classes.
The worrying news emerged from a survey of 18 primary schools, which found 24 children did not know how to use the toilet and still wore nappies.
One school reported having to replace the carpet in two classrooms because children had not got to the toilet in time.
Kent Community Health NHS Trust, which carried out the study, is now asking school nurses and health visitors to try to help children before they start school.
The initiative has been launched in nurseries in Dover and Deal but is likely to be extended across the county.
School nurse Chris Beer said: "Last year we had lots of contact from schools saying they were seeing a rising number of children starting school who were still wearing nappies and children who were not staying clean and dry during the day.
"Teachers were concerned they were spending less time teaching and more time helping children who were having accidents. Because some children don't drink enough, they don't learn to control their bladders and recognise the feeling of needing to go to the toilet.
"What we hope is that by working with children who are struggling in nursery we can support them so by the time they get to school they will be clean and dry and can concentrate on learning."
The Association of Teachers and Lecturers said: "It ought to be the parents' responsibility but there are some who lack parenting skills. Because the children are in school it's then left to teachers to deal with the situation."