An unremembered event, probably. The infant would be at least 94 years old, the boy might be over 100. What's left of this glorious summer's day, other than this photo?
The last living veteran of World War I died last year, so the soldier and sailors are certainly gone. There might be some of the clothes still around—a uniform may have been saved. A better chance of survival would be afforded the mandolin—an instrument which could conceivably be the very same one which now resides in Flippist World Headquarters!
The resort building behind the group might still be there, but its uninspired architecture and cheap construction make that seem unlikely. But the lake probably still exists, as well as the sun and the grass and all those other things which can turn a fine summer day into a memory for a lifetime.
Or, in this case, two lifetimes.
Image from the Luella Busch album, circa 1919