Children eat more than 10 pounds of sugar each year if they're eating a normal bowl of breakfast cereal every day, according to the Environmental Working Group.
The group found cereals for children had more than 40 percent more sugar than cereals for adults.
"Most pack in so much sugar that someone eating an average serving of a typical children's cereal would consume more than 10 pounds of sugar a year from that source alone," the group said.
Some leading cereal makers say they have cut back on the amount of sugar for children. But kids on average still eat two to three times as much sugar every day as they should, EWG said.
"The vast majority are still too sweet to be healthy, averaging two teaspoons per serving," EWG said.
EWG's latest analysis of sugary cereals showed that the ones with cartoon characters on the box are the ones most heavily loaded with sugar, with 34 percent of the calories coming from sugar.
One serving can equal the same amount of sugar as three Chips Ahoy! Or two Keebler Fudge Stripe cookies.
EWG surveyed 1,556 cereals, including 181 marketed for children. It also reviewed a sample of 84 popular kids' cereal they had looked three years ago to see if the sugar content had been lowered.