6yo asking for YouTube constantly - how do I make it stop?

My son just turned 6 and discovered YouTube Kids. Now it's ALL he wants. Every time we're in the car, waiting at the doctor's office, literally anywhere with downtime he's asking for it. I'm not totally against screen time but this is getting ridiculous. We're limiting it to 30 mins on weekends but that doesn't seem to be working as a deterrent. Anyone else dealing with this? What actually worked for you?