There were 2,456 children under 16 seriously hurt or killed on Britain's roads last year - and many councils have already imposed 20mph zones near schools.

But Brake said two-thirds of parents reported that some roads near their kids' schools had higher limits.

One example cited was Dropmore Infant School in Buckinghamshire, where nearby roads have limits up to 60mph and some areas have no pavements.

Head teacher Gitta Streete has called for 20mph limits for several years.

"One parent had their car door taken off by a passing car. That could easily have been a child, parent or carer being hit," said the head.

"What we need is a proper, phased speed reduction system: a reduction to 20mph outside the school and safe areas for everyone to walk along and cross the road."

Buckinghamshire Council's member for transport said it took road safety "incredibly seriously" and was aware of the school's concerns.

"We want to continue working as closely as possible with them and all schools to ensure all students have safe passage to and from school," said Steven Broadbent.

Brake said the situation is a common one and that teachers "need support from their local council and decision-makers".

"Why do we have to wait until a child is killed before we act?" said the charity's Lucy Straker.

She said it was a simple fact that "reducing speed saves lives" as a crash at 30mph has twice the amount of kinetic energy as one at 20mph.

However, one report from last year suggested cutting speed limits to 20mph in built-up areas did not significantly improve safety.

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It comes as pupils from more than 700 schools and nurseries will take part in Brake's Kids Walk today to raise awareness of the issue.

Wales is bringing in a default 20mph on residential roads and busy pedestrian streets on 17 September.

It says it will make it "one of the first countries in the world, and the first nation in the UK" to introduce such laws.

However, the Local Government Association, which represents councils, said it's up to each council to make speed decisions based on their own local needs.

A Department for Transport spokeswoman also said it was the decision of local authorities in England to choose their own limits and there were no plans to bring in any default or national 20mph zones.