(CNN) When children open their kids' meals from McDonald's or Burger King, they're probably looking forward to one thing the most: the plastic toy inside.

However, if these two children are successful, that will be a thing of the past.

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Sisters Ella and Caitlin McEwan, ages 9 and 7, started a petition to call on the fast-food giants to stop putting plastic toys in their kids' meals. The girls say they were spurred to act after they learned in school about the harm that plastic does to wildlife and the environment.

As of Wednesday, the petition had over 343,000 signatures, with a goal of 500,000.

"We know our young guests really enjoy their King Jr. meals, and we are working on the development of more sustainable packaging and alternative toy solutions," Burger King said in a statement. The company has pledged to have a more sustainable toy solution in place by next year.

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