A "rising number" of children are starting school still wearing nappies, say health experts in Kent.
Of 18 schools investigated, 24 children did not know how to use a toilet and still wore nappies.
Kent Community Health NHS Trust said some children did not drink enough water and did not recognise the feelings of a full bladder.
Modern nappies, which keep a child feeling dry for longer, have also been blamed for a delay in potty training.
Janet Marsh, a health visitor practice teacher, said parents "should not be blamed" for the delay.
"In the days of terry towelling nappies, if the child was wet it was uncomfortable," she said.
"Today with modern nappies they can stay in them so much longer and feel dry.
"Because of this, the child and parent can sometimes miss the cues that the child is ready to potty train"
'Not staying clean'
Teachers said they were spending more time dealing with children who were "having accidents".
A scheme to tackle the issue has been started in Dover and Deal.
The scheme will see school nurses and health visitors identify children who need help at nursery before they start school.
School nurse practice teacher 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 the children who were having accidents.
"One school told us that due to the problem, they had to replace the carpets in two classrooms."
It is working with two nurseries attached to Bright Sparks Preschool, in Deal, and Shatterlocks Infants School and Nursery, in Dover.