Serious question (I don't have kids of my own): before smartphones and tablets and the ubiquity of laptops and computers, what did parents do to get some peaceful time to themselves?

It's hard to believe that parents were only able to achieve this during the past 15-20 years.

(When I was a kid in the 80s and 90s, I spent plenty of time outdoors with my friends in the neighborhood, and also inside, in front of my Nintendo, either with friends or without. Not sure how much peace my parents got, but I assume it was non-zero.)

Same thing they do now: Get a nanny, ask the grandparents, playdates, ... Putting kids in front of a device is lazy, and unfortunately, most of us are lazy.

What era are you talking about? Later than the 90s had computers and game consoles. Before that it was going outside and digging holes, throwing stones.