The one sweet that parents were happy to buy their kids – because it did exactly what it claimed to do . . . stopped your gob from speaking/moaning/complaining.
Gobstoppers were massive and filled your entire mouth. They couldn’t be crunched or chewed because they were just too solid. Which is why Americans called them “Jawbreakers”.
You can still buy them, but they’re not as popular these days – mainly because they are unquestionably a choking hazard. Henry Heimlich introduced his famous manoeuvre in 1974 just as gobstoppers were at the height of their popularity. It doesn’t take a genius to make the connection there.