Back in the day we had a Mazda MPV mini-van and we drove the crap out of it, almost 200K miles before we traded it. My youngest son had his booster seat when he was a toddler and we would be driving along and we would hear crunch-crunch-crunch from him and I would say to my wife, Stephen is eating something and we didn’t bring anything from the breakfast/lunch etc... with us. She would turn around and catch him digging a crusty old McDonalds french fry out of one of the many hiding places in the seat to eat and she would have to take it away from him and toss it out the window.
They are pig poos. My wife would come back from a day out with the kids, I’d look at the seat and floor and say “Did they actually get anything down into their stomachs?”