The findings come in a poll of around 2,000 working parents of children aged four to 16, commissioned by Kellogg's.
It also concludes that some youngsters would be more likely to start school hungry if there was not a club available to give them a meal, while some parents say the lack of such a group would mean they would have to stop working.
The poll reveals that 17% of parents said their children would be left unsupervised for some part of the morning without their breakfast club, while nearly one in 10 (9%) admitted their sons and daughters would be less likely to get breakfast.
Around three in 10 (29%) said that they or their partner would have to stop working if their child could not attend a breakfast club and 15% said they would not be able to afford alternative childcare for their child in the morning while they were working.
Amongst families with children aged four to 11 and an income of less than £40,000, almost one in four (23%) said that their youngsters would be left alone for part of the morning.
The poll also found that nearly a quarter (24%) of working households use pre-school breakfast clubs to drop off primary school children before the bell goes so that they can get to work on time.
It also suggests that working parents who do not have access to a pre-school club have had to take measures such as arranging flexible working hours, taking a pay cut or putting their career on hold.
Paul Wheeler, a Kellogg's director, said: "For millions of parents in Britain, having access to a breakfast club helps them do the basics - keep down a job. But, with school budgets squeezed, it's more important than ever that breakfast clubs stay open."
The YouGov poll questioned 2,000 working parents with children aged four to 16 between January 27 and February 10.