Teachers must stop trying to wrap children in cotton wool with over-the-top health and safety policies, the chief inspector of schools has said.
Writing in the Sunday Telegraph, Amanda Spielman said it stopped the children developing resilience and grit.
She wants the education watchdog Ofsted to prepare new guidance for schools inspectors in England.
Ms Spielman said making pupils wear high-vis vests on trips made them look like mini-builders minus the hard hats.
She said schools had developed an over-cautious culture that made it difficult for young people to cope with everyday events.
While individual schools have imposed bans on playing conkers and on pupils bringing toys such as yo-yos over the years, the Health and Safety Executive point outs there has never been official regulation.
And Ms Spielman said every minute enforcing bans on conkers and yo-yos was a minute away from tackling a multitude of real dangers.
"I want Ofsted to make sure that schools are properly focused on pupil safety but that it doesn't come at the expense of opportunities to broaden and enrich young minds," she said.
"My message to schools is this - keeping children safe from harm should always be your overriding concern but in doing so make sure you distinguish between real and imagined risk.
"Trying to insulate your pupils from every bump, germ or bruise won't just drive you to distraction, it will short-change those pupils as well, limiting their opportunity to fully take advantage of the freedom of childhood and to explore the world around them."
Next month, 1,800 school inspectors will take part in sessions to ensure they focus only on the safeguarding of vulnerable children.
Ms Spielman said she looked forward to seeing more eager young faces on trips in the next school year but hopes "fewer of them will be auditioning for Bob the Builder".