Tell 'em that when people drank together (which actually has to be mentioned because a good portion drank by themselves), they always passed around a bottle, multiple bottles.
Groups always drinking out of the same bottle. Probably still a practice until today, at least in some parts by some creatures.
___
BTW, those playgrounds over there and other places in the early days were at times extremely dangerous. Going down a slide could rip a limb off because of no maintenance to what the metal/etc. turns into.
A typical practice in the USSR was a "troika". The vodka bottle size most frequently sold was 500mL, enough for three people to get a little buzz, while sharing the expense of ~ 3.62 for Moskovskaya or 4.12 for Stolichnaya (1970's) . In the photo just above, they're drinking cheap fortified wine (most popular labels were Agdam and 777), not dissimilar to Ripple, Thunderbird or Night Train. Those had alcohol content of about 18%, which made disease passing a low risk. Just in case, there was a manner of drinking from a common bottle, which was to attach the outside of the lips only. The next inline would then try to smudge the traces of the previous drinker from it.
And, while we didn't have a slide in our building, we did have a sand pit. However, my favorite sand pit was a block away at my old elementary/high school. We had a stadium there and the pit for long jumps. Which was perfect for playing a soccer goalie, as one could dive freely without hurting oneself.
Old style vodka bottles.
https://st.violity.com/files/2012/02/21/20/33133_1329847964.jpg














