Up to 220 young children a day may be exposed to potentially dangerous levels of pesticides just by eating an apple or a pear, say researchers.
There is controversy about what pesticide level is safe
The charity Friends of the Earth based its calculation on government data on pesticide levels on fruit.
However, the Food Standards Agency has insisted that pesticide residue levels are safe.
The study is published in the International Journal of Occupational and Environmental Health.
The researchers say internationally agreed safety levels on pesticides can be breached even when legal limits are met.
They found imported produce was more likely than home-grown fruit to contain high pesticide levels.
The government regularly monitors pesticide levels in fruit - but tests blended batches, rather than individual items of produce.
Friends of the Earth say research has shown that pesticide levels can vary widely from one piece of fruit to the next.
Call for action
Report author Emily Diamand said: "Parents will be shocked to discover that pesticide safety limits set to protect young children can be exceeded just by a child eating one apple or pear.
"The problem of high residues occurring in individual fruits or vegetables is well known to the government but they continue to issue bland reassurances that there is no risk to health.
"This problem must not be ignored any longer.
"The government must act quickly to make sure that legal limits for these pesticides protect consumer safety and do more to help farmers reduce their pesticide use."
The study focused on the pesticides carbendazim, dithiocarbamates and phosmet, which is not licensed for UK use so only occurs on imported fruit.
Carbendazim and dithiocarbamates are suspected of disrupting hormone function.
Phosmet is an organophosphate insecticide, which has the potential to damage the nervous system and is a potential carcinogen.
Friends of Earth say while there may be no obvious immediate effects from consuming these chemicals at high levels, there may be long term implications.
Children are particularly susceptible because they are still growing and developing.
Professor Andrew Watterson, of Stirling University who also worked on the study, said: "Very little is known about the long term effects on the immune, hormone or nervous systems when young children are exposed to short term high levels of pesticides.
"But the pesticides found in this research all have the potential to cause damage to health.
"The government must take a precautionary approach and ensure that internationally agreed safety limits are not breached."
Because legal limits were not exceeded, apple growers would not have been alerted to any problem with levels of pesticides in their fruit.
Friends of the Earth wants the government to take urgent action to lower legal limits to ensure safety limits are not breached.
David Budd, a member of the British Independent Fruit Growers Association said: "I'm concerned that it appears from this research that safety levels for apples and pears could be breached even when legal limits have been met.
"We go to great lengths to minimise inputs and are pleased that these efforts are reflected in the results that show English apples and pears are a safer option than imported."
'Don't stop eating fruit'
Friends of the Earth is urging parents not to stop giving apples and pears to their children, as fresh fruit is an important part of a healthy diet.
A Food Standards Agency spokesman also said it would be "unfortunate" if the study deterred parents from encouraging their children to eat fruit.
"We have only just seen this paper, but it appears to present an unrealistic scenario of children regularly eating fruit with high levels of pesticides," the spokesperson said.
"That is not to say that the agency is complacent. Maximum levels of residues allowed in foods are generally set well below the safety limit giving an additional margin of protection.
"Levels of pesticides currently found in food are not a safety concern, if they were the agency would take immediate action."