fidget/sensory toys? and is there a classification that would be given to a book on the period of time in which fidget spinners were a major fad?
There's no category for fidget toys specifically, but toys in general fall under 790.133, and books on fidget spinners have been placed there or 793.4 for "action games." The time period, mid-to-late 2010s, would be under 973.932 and 973.933 (though most of those are about political/governmental/civic history rather than social history/fads)