Four nursery workers have been arrested on suspicion of child cruelty after a two-year-old was allegedly assaulted.
Police attended Lemongrove Nursery in Bromley, south-east London, on 20 May following the alleged incident.
Detectives arrested four women, aged between 18 and 28, on suspicion of child cruelty before they were released on bail.
Another two staff members were interviewed voluntarily by detectives.
The nursery is no longer operating, the force said, with enquiries from the Metropolitan Police’s Child Abuse team continuing.
Schools watchdog Ofsted said the nursery was suspended between 31 May and 12 July.
It added it was initially closed so the watchdog could probe claims a child may have been exposed to risk of harm.
A Met Police spokeswoman said: "We can confirm police are investigating allegations of child cruelty in relation to a nursery school in Bromley.
‘’It is alleged that on Friday May 20 a two-year-old child was physically assaulted by staff members at the venue. There were no apparent physical injuries to the child.
"Four female members of staff, aged 18 to 28, have been arrested on suspicion of child cruelty and were subsequently released on bail.
"Two further female members of staff were interviewed voluntarily."
She added: "Enquiries are ongoing. Detectives from the Met’s Child Abuse Investigation Team are investigating.
"We are aware the nursery is no longer operating.’’