Answering your questions in turn, in late 1950s USA kids didn't play soccer. Yes, I'm sure soccer was played in Hispanic and immigrant communities, but we wouldn't have known. I'd be surprised if half the kids in my grade school (including me) had any idea what soccer was. It's hard to imagine how insular middle-class, small- and medium-town Americans were in those days.The closest we came to soccer was kickball, with two teams running around kicking at a ball midway in size between a basketball and a soccer ball but "bouncier" than either.
We saw mercury exhibited as a curiosity in science class, but weren't allowed to play with it ourselves. There was a scientific supply shop in the nearest big city, but only science teachers went there. We weren't the adventurous sort who'd persuade a stooge to buy mercury for us. We weren't even determined enough to smash a hundred thermometers to acquire a small stash. Like so many of our grand childhood ideas mercuryball was a languid fantasy.
I didn't know you were American, Crash. Most of the posters active on This forum seem to be English, Scots, Australians, Canadians, or European. I assume Narfstar is American (but am not quite sure).
Yes, growing up in Canada during the late 1940s and '50s, and early 1960s, we didn't play "soccer" at all. I did play soccer(football) in Holland when we were there. We also played Canadian Football as kids , with teams 12 a side, and 3 downs per possession, and 1 point for a Rouge on a punt. Canadian Football evolved out of Rugby Football, which was the most popular Football-related game in Canada, and 3rd most popular sport, after ice hockey and Lacrosse. It was very recently when I was young 1948, that The Canadian Rugby League changed its name to The Canadian Football League.
Apparently a similar evolution had taken place in USA, only much earlier, with Rugby Football morphing into American Football by rule changes, first allowing the ball to be handed of or shoveled forward, and later, thrown overhand (passed) forward on offence. Those two changes probably happened some time in the 1890s and 1910s in US College football, and the first change, during the 1930s in Canadian Rugby.
I assume that some time in the late 1800s, people in Rugby, England, started changing the rules of Football, and Rugby Football evolved into a separate sport.
As for myself, I grew up playing mainly ice hockey, as we had long, long winters in Manitoba, back before Global Warming, with 4.5 to 5.5 months of snow and ice on the ground, with no thaw, and lots of frozen lakes and ponds on which to skate. My uncle, who lived next door to us, was a youth hockey coach, and my father and he took out the fence between our backyards, and made one large ice rink every Autumn. We had wooden walls, and every mid to late October, we we would lay down a large tarpolin, and start laying down layers of hose water, letting it freeze over the previous one, until our rink was thick enough. We had a hand push ice grader for smoothing. I played and or practised virtually every day for half of every year. I started playing in organised leagues at 6 years old, and got up to making a team at the highest level of amateur hockey, whose teams were sponsored by the professional leagues. Soon after, my parents moved to USA, and, at age 16, I had to decide whether to move with them, or stay with my uncle and aunt to pursue a potential hockey career. I moved with my parents, hoping to get a scholarship to play at a US University, but Chicago, at that time, didn't have a high enough level of Junior Hockey to allow me to be seen by scouts to earn a scholarship.
I played some (Canadian) Football, Baseball, and skied as a youth in Canada, played Football(Soccer) as a child in Holland (I spent every summer there as a youth). And as an adult, I was a recreational back-country skier, and played in recreational Football(Soccer) leagues in Denmark and Jordan. when living and working there.
I sincerely doubt that a chemist(pharmacist) would have been allowed to sell mercury to a minor ( or, at least, person under 18 years old) in Canada when I was growing up. It is a toxic and hazardous substance.