Many U.S. families choose fast-food restaurants because the meals are cheap, easy and they often are a reward for their children, researchers say.Kerri N. Boutelle of the University of California, San Diego, and Rady Children\'s Hospital-San Diego, say adults overwhelmingly reported that they liked the food, while 49 percent say the toys include with the children\'s meals was not the top reason for eating at the fast-food restaurant.Parents trade convenience of fast-food for meals that provide 36 percent to 51 percent of a child\'s daily caloric needs, which may contribute to obesity.In addition, the study, published in the journal Childhood Obesity, lunchtime-meals had more than 50 percent of the recommended total daily sodium intake for most children, while some had 100 percent of sodium levels recommended for preschoolers, the researchers say.The researchers surveyed 544 families with children entering a fast-food chain restaurant located inside Rady Children\'s Hospital in San Diego at lunch time over a six-week period. Families were asked to retain and present their receipts from food purchases and complete a brief survey.\"The number of meals and snacks eaten away from home is believed to contribute to excess calories consumed by children, and this number has increased dramatically in the past 30 years,\" Boutelle says in a statement. \"On a typical day, a remarkable 30 percent of youth report consuming fast-food.\"