How many of us boomers (not old-timers) played with mercury from broken thermometers in the late 50s?

A great many: Pure mercury, of type you're describing, is not toxic, and one can play with it and even swallow it with impunity. It's mercury oxides and other related compounds that potentially can produce significant toxicity--and it oxidizes readily if left out in the open air. The debate is, what kind of damage can it do over time , especially is low doses. Evidence suggests not much.