Police were alerted after a man was found trying to talk to children through a school gate on Monday.
The incident took place outside Avon House Preparatory School in Cromer Road, Woodford Green at about 1pm.
The man was seen walking off towards Buckhurst Hill.
Headteacher Amanda Campbell said: “We called police and we checked the vicinity and the pub nearby – we telephoned local schools to tell them so they could be extra vigilant.
“At no point were the children at risk or was he on school premises.”
A Metropolitan Police spokeswoman said: “Police would ask parents and teachers to remind children the importance of not talking to or going with strangers.
“To report anyone acting suspiciously call police on 101, in an emergency call police on 999.”
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