The head of the Ofsted education watchdog in England will highlight in a speech the rising number of young children who lack basic hygiene skills.
Amanda Spielman will describe how a lack of toilet training is disruptive for teachers and can have a negative effect on a child beginning school life.
She will highlight a recent study which found 70% of schools reported more children starting school without being toilet trained compared to five years ago.
She will also claim an increased number of young children cannot communicate properly.
Ms Spielman is due to tell the pre-school learning alliance: “We now have a situation where, aged four, some children have less than a third of the English vocabulary of their peers.
“These children arrive at school without the words they need to communicate properly. Just imagine the disadvantage they face, right from the start.
“Unable to follow what’s going on. Unable to keep up with their classmates. Unable to reach their potential.”
She will encourage daycare staff to spend time teaching pre-school children new language skills – whether through songs, nursery rhymes or “time-honoured classics” such as Hans Christian Andersen or Dr Seuss.
“We know that at the most basic level, poor literacy holds a person back at every stage,” she will add.
“As a child, you will do worse at school. As a young adult, you may struggle to find work. And as a parent, you won’t be able to help your own children learn. This is a vicious cycle.”
She will also stress: “I am not suggesting nurseries are substitute parents.
“Nor do I think children should start reception as perfectly well-turned-out mini adults, who always go to the toilet unaided and never have accidents.
“But we know that the best nurseries work closely with families, helping to establish simple routines, such as sleep time and potty training, as well as introducing children to foods that they may refuse at home.”