The WHO said local restrictions could be needed if cases continue to climb.
Parents are being advised to reduce their children's activities over the remainder of the Halloween midterm.
The Deputy Chief Medical Officer says precautions should be taken to the recent rise in Covid-19 cases.
4,393 cases were reported in children aged 5-12 in the two weeks to last Monday.
That's compared to 2,930 over a similar period earlier this month.
Dr. Ronan Glynn says trick or treating can still go ahead but reducing frequency needs to be considered.
Meanwhile, Dr David Nabarro, the WHO's special envoy on Covid, says local restrictions could be needed if the trend continues - but not a national lockdown.
