Kourtney Kardashian complained to her children's school about the food they serve.

The 'Keeping Up With the Kardashians' star - who has Mason, nine, Penelope, seven, and four-year-old Reign with former partner Scott Disick - ''wasn't satisfied'' with the processed meals being dished out at lunch time so had a meeting with the principal.

And that was just the start of Kourtney's complaints as the 40-year-old star is determined to campaign for ''small changes'' that have ''big impacts'' on her kids' lives.

She wrote on her lifestyle website Poosh: ''I wasn't satisfied with the food being served at my kids' school, so I made sure that the principal knew my concerns.

''I've continued to offer my two cents on everything from the type of milk they serve to their use of single-use plastic.

''I've found that simply using my voice to stand up for small changes that add up to big impacts is so effective at not only creating change, but setting an example for my children.''

And Kourtney called on other mothers to do the same.

She wrote: ''I may not be the loudest or the most aggressive, but I've never been one to stand by and watch something I disagree with unfold.

''As moms, it's in our power to raise some awareness and rally for healthier options. I'm doing it for my children and their futures.''

In another recent post on Poosh, Kourtney wrote about how she's been stressing the importance of sustainability to ker kids and thinks it's vital the next generation have ''fundamental values'' that will help the planet.

She wrote: ''I'm constantly sharing with my kids the importance of sustainability.

''While sometimes it feels like it's 'too late' for my own generation to get on the same page, we can form a new generation that is raised in awareness about the state of the world -- a generation with fundamental values that promote sustainability.''