The study included three McDonald's menu items — hamburgers, chicken nuggets and french fries — and store-bought milk or juice and carrots. Children got two identical samples of each food on a tray, one in McDonald's wrappers or cups and the other in plain, unmarked packaging. The kids were asked if they tasted the same or if one was better. (Some children didn't taste all the foods.)

McDonald's-labeled samples were the clear favorites. French fries were the biggest winner; almost 77 percent said the labeled fries tasted best while only 13 percent preferred the others.

Fifty-four percent preferred McDonald's-wrapped carrots versus 23 percent who liked the plain-wrapped sample.

The only results not statistically clear-cut involved the hamburgers, with 29 kids choosing McDonald's-wrapped burgers and 22 choosing the unmarked ones.

Fewer than one-fourth of the children said both samples of all foods tasted the same.

Pradeep Chintagunta, a University of Chicago marketing professor, said a fairer comparison might have gauged kids' preferences for the McDonald's label versus another familiar brand, such as Mickey Mouse.

"I don't think you can necessarily hold this against" McDonald's, he said, since the goal of marketing is to build familiarity and sell products.

He noted that parents play a strong role in controlling food choices for children so young.

But Robinson argued that because young children are unaware of the persuasive intent of marketing, "it is an unfair playing field."