Ayds contained a substance that was supposed to reduce the sense of taste and therefore appetitie (although anyone with a cold knows that numbing the sense of taste doesn't always reduce appetite). Since you were supposed to take them with a full hot cup of liquid (like tea or coffee or even hot water), before eating, the liquid no doubt helped to curb appetite more than the candy itself.
When I was about 5, I got into my grandmother's box, and had eaten half dozen of them or more before I was found. My mother called the doctor and she was told there was nothing to worry about. When I used them the "right way" as a teenager that was always in the back of my mind - if they were safe for a child to eat in bulk, how effective could they be.