The study for environmental charity Global Action Plan said kids are nearer to exhaust pipes of vehicles and therefore ingest more pollutants such as particulates.
For children inside cars stuck in traffic the problem is even worse – they are exposed to twice the level of pollutants as those walking, even along busy roads.
For the research, children and adults across four UK cities – Manchester, Leeds, Glasgow and London – carried an air pollution monitor for 10 minutes while walking along a quiet route, a busy road, a journey by car in traffic and on a bus.
Chris Large, from Global Action Plan said: “Millions of children in the UK that are walking to school along busy roads are potentially being exposed to 30% more pollution than their parents.
“A simple solution for parents would be to choose quieter back routes to walk or cycle their children to school, away from the traffic, thereby reducing their exposure to unnecessarily high levels of damaging air pollution.”
A separate study by Unicef UK has suggested that one in three children could be susceptible to long-term health problems because the areas in which they live have such high levels of pollution.
Amy Gibbs, Unicef UK’s director of advocacy, said: “Worryingly, one third of our children could be filling their lungs with toxic air that puts them at risk of serious long-term health conditions.
“We wouldn’t make our children drink dirty water, so why are we allowing them to breathe dirty air?”