The plastic toys given away with children's fast food meals are under fire. McDonald's and Burger King are the target of a petition started by two British school children who criticize the companies for giving away the toys that they say are put in the trash after only being used briefly. McDonald's Happy Meal and Burger King's Kids' Meal include a main meal, side, drink and a toy, which is often linked to movie releases. "We like to go to eat at Burger King and McDonald's, but children only play with the plastic toys they give us for a few minutes before they get thrown away and harm animals and pollute the sea," wrote Ella and Caitlin Wood on a Change.org petition page, which has more than 335,000 signatures. The children, aged 9 and 7, wrote that they learnt about pollution at school and recycle at home. "But we want to do more, which is why we started this petition. It's not enough to make recyclable plastic toys — big, rich companies shouldn't be making toys out of plastic at all," they wrote.

In the U.K., McDonald's has set up a group to explore "more sustainable" toy options, it said in a statement emailed to CNBC, and last year it started to replace plastic straws with paper in its British restaurants. "We want anything they give to us to be sustainable, so we can protect the planet for us and for future generations," the children stated in their petition. McDonald's introduced the Happy Meal in 1979 to appeal to families. The meals were popular with children because they could choose what they wanted to eat, from packaging that was designed especially for them. The meals' contents have changed over the years, with Chicken McNuggets introduced in the 1980s as diners sought to reduce their fat and cholesterol intake. Last year, Disney announced a new partnership with McDonald's after a 12-year gap, following a revamp of Happy Meals to reduce their sugar, saturated fat, sodium and calorie content. In a statement emailed to CNBC, a McDonald's spokesperson said that there would be a reduction in the number of "hard plastic" toys given away in the second half of the year, due to a trial to see what kind of toys diners prefer. "However, this is not indicative of a new commitment to reduce plastics in Happy Meal toys. This six-month promotional period in the U.K. will provide different options to customers including a mixture of board games, books and soft toys," the statement said.