OKLAHOMA CITY -- Several metro middle school students were sick Friday night after eating food that had been left out since before Christmas.

Cafeteria workers at Western Oaks Middle School, in the Putnam City school district, on Northwest 23rd Street made the mistake, officials said. According to reports, the workers left behind a tray of about 25 burgers inside a warmer.

When school resumed after the holiday break, that food was mixed with fish sandwiches and served to students.

Officials said they took immediate action to get the bad food out of the cafeteria rotation. However, 10 students took at least a bite of old hamburger. Some ate the whole thing.

Now, parents are concerned that their children will come down with food-borne illnesses. One parent said that doctors have told them there's a waiting period for some of the bacteria in the old hamburger to become present.

Sodexo Foods handles all the food for Putnam City Schools, and a spokesperson for the company admitted the mistake, saying the cooked hamburgers were left in the warmer. Fish was then stacked on top of the bad hamburger, and because both were wrapped in foil, workers didn't notice the difference.

Officials said they were considering doing some training and retraining with employees to ensure this never happens again.

However, education is not enough for some parents.

One parent said, "And I think personally that some heads should roll. I think that they should fire the entire cafeteria staff. Dismiss everybody on that staff."