Happened to us once at a Burger King. We were in a large group packed into several vehicles. When we got home 15 minutes later was when we realized we lacked one child. Worse moment of our lives. Immediately called manager while others rushed back to restaurant. People eating there saw us leave without child and waited for us to realize it and return.
I did the same thing. We were in Yellowstone with all our kids, their kids, and our thirteen year old. Also with us was a cousin with her husband and her daughters. We were in 3 different vehicles near Mammoth, and there was NO cell phone coverage at the time. I thought she was with my son’s van, he thought she was in our van. But she wound up getting in the van with my cousin. Never alone actually, but I felt like an IDIOT.
It happened to Mary and Joseph once too, but it was all good.
I came from a large family myself. We took family vacations in a station wagon. My kid brother, maybe 6 years old at the time, was asleep when we stopped for gas once and, after everyone had their potty break, we all piled back in the car and were about 15 minutes down the road before I noticed him missing.
Dad did a U Turn and drove back in a panic. He was sitting in the gas station lobby happily slurping an orange soda someone had boughten for him. We asked if he was worried and he replied "No, cuz I knewed you'd come back."