A nursery worker has been arrested over claims that he mistreated a two-year-old boy in his care.
The 21-year-old was questioned by detectives after concerns were raised over an incident in Twickenham, south-west London.
A file of evidence brought together by child abuse investigation officers has been passed to prosecutors.
The Sun reported the suspect faces claims he hit the boy's privates with a plastic ruler after he wet himself.
It is also alleged he slapped the boy over the head with some plastic gloves, but the carer insisted he was tickling him.
A spokesman for the nursery said the man has been sacked and a second member of staff suspended.
He said: "We very much regret this situation. Our number one priority is the safety and wellbeing of every child in our care and we immediately notified the child's parents, Ofsted and the local safeguarding team, which includes the police.
"We also immediately suspended two members of staff. A full investigation was carried out.
"No harm has come to the child concerned but one member of staff has since been dismissed. The matter is with the CPS for it to decide what further action, if any, should be taken."
A Metropolitan Police spokesman said: "We can confirm that we have received an allegation of assault on a two-and-a-half-year-old boy at a nursery in Twickenham.
"The incident is said to have taken place on January 18 and was reported to police following a meeting with the parents of the child and the nursery.
"The matter is being investigated by the child abuse investigation command based at Feltham.
"A 21-year-old man attended Teddington Police Station by appointment on January 22 and was arrested. He has since been bailed pending further inquiries.
"A file has now been submitted to the Crown Prosecution Service for consideration."