Around one in four parents know of a child in their area who may be going hungry, a survey has found.
The poll suggests that the problem may be getting worse, with many parents saying they have seen an increase in the numbers of youngsters they are worried about.
But it also reveals that many are reluctant to get involved, with more than half failing to report their concerns to the authorities.
The survey, conducted by parenting website Netmums and Kids Company, questioned more than 1,100 people to mark the launch of their new Mobiles for Meals campaign.
It encourages the public to donate their old mobile phones to feed a hungry British child.
The survey found that a quarter of those questioned said they were aware of children in their area who might be going hungry.
Of these, more than one in four (27.8%) said they had seen an increase in youngsters they were concerned about in the last two or three years.
Almost a third (31%) of those who said there was a child they were worried about said they had reported their concerns to someone in authority, such as a school.
But 53.2% revealed they had said nothing because they either were not sure enough of their concerns, or did not feel it was their place.
The survey also asked parents who were concerned about a child for the reasons why they thought the youngster may be suffering from "food insecurity".
Around three-fifths said they thought it was because the family did not have enough money to buy the food they needed, while a similar proportion said they thought it was because the family was buying low quality food as they were short of cash.
More than half (55.4%) said that it was because a parent was abusing drugs or alcohol which meant the child was being neglected.
Netmums co-founder Siobhan Freegard said: "This campaign is about mums across the UK taking this unacceptable situation into our own hands.
"Too many children are not on the breadline, they are way, way under it.
"It's horrifying to realise how many kids are suffering around the UK.
"They are having their chances ruined before their lives have barely begun."
Speaking to The Huffington Post UK in April Camila Batmanghelidjh said she had seen children who are so malnourished they have lost teeth.
:: The Netmums survey questioned 1,116 people between June 18 and 22.
A government spokesman said: "We are tackling child poverty by extending free early education, investing to help families with childcare costs and introducing universal credit which will lift hundreds of thousands of people out of poverty.
"Work is the best route out of poverty which is why the Work Programme will ensure that people receive the personalised support they need.
"All children from the poorest families are entitled to receive a free hot meal at school every day. We have launched a review to make sure that healthy and nutritious school food is available to all children."