Ella and Caitlin McEwan first launched their petition on Change.org nine months ago.
In the petition's blurb, they explain that they have been learning about the detrimental impact of plastic waste, which is why they want McDonald's and Burger King to "think of the environment and stop giving plastic toys with their kids meals".
In June, the pair appeared on BBC One programme War on Plastic with Hugh and Anita, in which they revealed that they had amassed more than 160,000 signatures, with a target of reaching 200,000.
However, one month on, the schoolgirls' target has been increased to 500,000, an objective which they are just under 100,000 signatures shy of achieving.
In an update published on the petition's webpage a week ago, Ella and Caitlin explained that they had received "lots of media attention" across the world, including in the US and in Germany.
"Hopefully this will create lots more interest and pressure on McDonald's and Burger King to make lasting changes," the sisters wrote.
Four months ago, the schoolgirls revealed they had received an official response from Burger King.
"We appreciate in our modern climate, plastic consumption is a big issue and is something we as a brand need to review," a Burger King spokesperson said in response.
"Whilst we can't advise of any changes at the moment, we have forwarded your comments through to our management team so we can review the matter."
Plastic waste across the world: in pictures
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According to the sisters, their response from McDonald's was an automated email.
Several individuals who signed the petition have commended the schoolgirls on their efforts to raise awareness of plastic pollution.
"These young people are already thinking ahead about the welfare of future generations. Thank you Ella and Caitlin!" one person wrote.
"Proud of you girls for fighting for the planet," another added.
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An eight-year-old boy from Essex recently wrote an open letter to McDonald's urging the fast food restaurant to remove plastic toys from its Happy Meals.
In the letter, Jacob Douglas wrote that he is concerned about the way in which plastic is "affecting the world around us".
In response, a McDonald's spokesperson said the company is "very impressed" in Jacob's passion for the environment.
"McDonald's is looking at alternatives that will keep our Happy Meals fun without causing damage to our environment," the spokesperson added.
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