WASHINGTON (Reuters) - Some breakfast cereals marketed to U.S. children are more than half sugar by weight and many get only fair scores on nutritional value, Consumer Reports said on Wednesday.

A serving of 11 popular cereals, including Kellogg’s Honey Smacks, carries as much sugar as a glazed doughnut, the consumer group found.

And some brands have more sugar and sodium when formulated for the U.S. market than the same brands have when sold in other countries.

Post Golden Crisp made by Kraft Foods Inc and Kellogg’s Honey Smacks are more than 50 percent sugar by weight, the group said, while nine brands are at least 40 percent sugar.

The most healthful brands are Cheerios with three grams of fiber per serving and one gram of sugar, Kix and Honey Nut Cheerios, all made by General Mills, and Life, made by Pepsico Inc’s Quaker Oats unit.

“Be sure to read the product labels, and choose cereals that are high in fiber and low in sugar and sodium,” Gayle Williams, deputy editor of Consumer Reports Health, said in a statement.

Honey Smacks has 15 grams of sugar and just one gram of fiber per serving while Kellogg’s Corn Pops has 12 grams of sugar and no fiber.

Consumer Reports studied how 91 children aged 6 to 16 poured their cereal and found they served themselves about 50 to 65 percent more on average than the suggested serving size for three of the four tested cereals.

Consumers International, which publishes Consumer Reports, said it would ask the World Health Organization to develop international guidelines restricting advertising and marketing of foods high in sugar, fat or sodium to children.

However, the group noted that breakfast cereal can be a healthful meal and said adults and children alike who eat breakfast have better overall nutrition, fewer weight problems, and better cognitive performance throughout the day.

Kellogg said it was working to make its food more nutritious.

“Kellogg recently reformulated a number of our cereals including Froot Loops, Corn Pops, Rice Krispies, Cocoa Krispies and Apple Jacks in the U.S. with improved nutritional profiles,” a company spokeswoman said by e-mail.

“To put Consumer Reports’ information in perspective, yogurt contains more sugar and sodium than a serving of Honey Smacks cereal (25 grams of sugar vs. 15 grams of sugar in Honey Smacks).”

Consumer Reports, like other groups, compares the sugar content of food with its fiber, mineral and vitamin content. Many cereals are fortified with vitamins and minerals.