Children are used to being told a trip is being postponed because of the vagaries of Britain's rainy summers.
Sports days should be early in the morning
But now schools in Derby are being told to consider cancelling trips in good weather because of the risk of sunburn.
Derby City Council issued the guidelines because of the link between sunburn when young and increased risk of skin cancer in later life.
It said teachers should consider "postponing or cancelling events... in periods of excessive sun".
The guidelines also advised to teachers to "try to plan external activities, for example, short duration trips, external lessons and sports days, for times when the sun is likely to be at its lowest strength - and the temperature at its lowest".
Teachers should also consider keeping a supply of maximum factor suncream to spray onto pupils, although they are told not to rub it in for fear of being accused of inappropriate contact.
The National Union of Teachers recently told teachers to take a "common sense" approach to protecting their charges from the sun in the face of increasing risk of legal action.
One parent told BBC Radio Derby: "People are going absolutely crackers - teachers should be able to take children out any time of the day or night, whenever they feel like it."
Another parent said: "I always put sunscreen on my little girl anyway, so I am not worried.
"They are making something out of nothing really."
A spokesman for the council told BBC News Online: "This was issued in response to requests from schools using government advice that is several years old already.
"We hope the result will be that children are protected from skin cancer not that children's activities are curtailed."