Growing up mercury was a favorite play toy. Everyone loved it and almost everybody had some. We would rub pennies in it and drop it on the floor then work the drops back together again, squeeze it between our fingers, just generally have fun with it.
2. Which is more dangerous, handling it with your fingers on relatively rare occasions or having it pumped into your blood multiple times during your developing years as a child by a doc and packing it into your mouth by a dentist?
Playing with it, without a doubt. The latter is not even close and simply nothing to worry about.
Quarantine was not something from just long long ago. Even when I was growing up it was normal to quarantine families where measles broke out. That also held true for things like polio, with pool closings and cancellations of any group activities.