The juice problem is easily preventable as long as you don't have a spouse who disagrees with a no-juice policy.
You'd also have to diaper kids for years after you'd normally consider them potty trained. Small ones don't plan ahead, don't tell you in advance, and aren't as determined to hold it as you might be.
You'd also need to have something to clean dirty hands.
In the end, you can probably get away with keeping your car clean by making it your thing. "No food, sit quietly in this car!" It's not a battle I'd choose to fight with my kids, but to each their own. It would be even harder with a couch, or other furniture that lives in your home.
I remain shocked at how many people eat in their cars, especially messy or aromatic Foods. I love in ‘n out, but I sure as heck don’t want the inside of my car to smell like it.
You'd also have to diaper kids for years after you'd normally consider them potty trained. Small ones don't plan ahead, don't tell you in advance, and aren't as determined to hold it as you might be.
You'd also need to have something to clean dirty hands.