Schools are being urged to review their planned trips in the wake of the recent terrorist attacks.
Heads from the Association of School and College Leaders will issue new guidance in the next few days on how schools should approach planned trips.
Its general secretary Geoff Barton says schools should review and amend risk assessments of trips as necessary, and take on board the views of parents.
It comes amid reports schools across England have been cancelling trips.
Year 6 pupils from St Michael's Church of England Primary Academy in Exeter have had a three-day trip to London due to start on Monday cancelled.
The school website said: "After the events in London on Saturday night, we have made the decision to cancel the residential. The travel company are working with us to try to re-book for later this term.
"We are sorry for any disappointment and inconvenience caused and offer our thoughts and prayers for those directly involved in the incident."
Pupils from Torre Church of England Academy in Torquay also had their trip to the capital cancelled because the pupils were due to stay just over the bridge from where the attacks happened.
And Kea Community Primary School and Devoran School near Truro in Cornwall had been due to send a class of Year 6 children to London at the end of the month.
However, head teachers at the two schools decided to put the trips on hold until "things settle down" after the weekend's tragic events.
ASCL leader Mr Barton said: "Our advice to schools concerned about planned trips to London is to review and amend risk assessments as necessary, and to talk to parents to gauge their views.
"Where school trips go ahead, parents who are concerned can withdraw their children.
Visits by some primary and secondary school pupils to attractions such as the Science Museum, Tower of London and the British Museum have been scrapped in the post-terror clampdown, the Guardian reports.
Pupils from RL Hughes Primary School in Ashton near Wigan also had their London trip, which included a visit to the Natural History Museum and the Hard Rock Cage, cancelled.
And some head teachers have been writing to parents asking their views on whether certain trips, especially those to central London, should go ahead.
"If schools choose to cancel trips, we would ask that people respect that decision, which will have been made after full discussion and in light of the individual circumstances.
"Each school works in its own distinctive context and will make decisions based on the best advice available."
His association will send out new guidance to member head teachers in the next few days.
A group of key tourism organisations - the Tourism Industry Emergency Response Group (Tier) - met on Monday to discuss the potential impact of recent terrorist incidents.
Bernard Donoghue, director of the Association of Leading Visitor Attractions, which is part of Tier, said: "We've had some city centre attractions saying some school and family groups have changed their plans and gone to places such as Bath and Canterbury, rather than London."
But he said there had been "very few" cancellations to visitor attractions by those coming from overseas.
It is inevitable that there may be some cancellations in future but the tourism industry has been reassured by the "measured" coverage of the attacks, Mr Donoghue said.
But he added: "There's a recognition that London has a proud, safe history and people are not taking the sort of knee-jerk reactions they they would have done at the height of the IRA bombing campaign."
Mr Donoghue added that the swift response of the Metropolitan Police to the London Bridge attack could also protect visitor numbers.