Campaign group Action on Sugar found some products made to appeal to children contained up to four teaspoons of sugar per serving.
It called for a ban on use of cartoons, vibrant colours and familiar characters on products with high or medium levels of sugar, salt and saturated fat.
Kellogg’s Frosties – which uses the smiling image of Tony the Tiger – was among the worst offenders, with 11g sugar per 30g serving.
Malt-O-Meal Marshmallow Mateys – containing colourful shapes and sold in a bright red box – topped the chart at 17g per 42g serving.
But health minister Will Quince said it was up to parents to teach their children about the importance of a healthy diet.
He told Times Radio: “I’m not in favour of those kinds of nanny state interventions because as a parent, it’s my responsibility to educate my child as to what is and isn’t appropriate for daily consumption and as a treat.”
“I like Krave cereal as much as the next person… it’s very nice, but would I have it every day? No, because I know the implications of that. I want to educate my children about that.”
“So what it means is we need to empower people to make healthier life choices.”
Mr Quince said plain packaging was “certainly a step too far” as they were enjoyable when had in moderation, and should be had “every now and then as a treat”.
Action on Sugar is based at Queen Mary University of London and regularly conducts product research.
Its investigation found that 65% of 73 yoghurts and 47% of 133 cereals surveyed contained at least one third of the recommended maximum sugar intake for a child aged between four to six years (19g or five sugar cubes).
Breakfast cereals and yoghurts saw significant reductions in sugar levels between 2015 and 2020, at 14.9% and 13.5% respectively.
But the Sugar Reduction Programme announced in the Government’s 2016 obesity plan set a target of 20%.
Registered Nutritionist Dr Kawther Hashem, campaign lead at Action on Sugar, said: “It’s ludicrous that whilst breakfast cereals and yogurts celebrate the largest reductions in sugars during the Sugar Reduction Programme, those same products with child-appealing packaging still have excessive amounts of sugars, unsuitable for regular intake by children.”
“Given the soaring numbers of under-18s suffering weight-related health problems and tooth decay being the leading cause of child hospitalisation, now is the time for companies to be forced to remove child-appealing packaging from products that are misleading parents and making our children unhealthy and sick.”