For instance, nowadays it's increasingly common for people to play games on their phones or browse Facebook for hours every day. In the early 1900s (say before widespread access to TV), was there some equivalent set of activities people in the US would engage in to the same degree? Was there concern, moral or otherwise, about some new activity children engaged in seemingly to excess?
A lot of people, in particular young adults, read comic books, and the public reaction to that was pretty much the same as it was with video games in the nineties. The particularly "violent" series, like DC's Batman and Superman had a lot of negative reaction among parents, with old school conservatives claiming the violence corrupted young minds (sound familiar?), to the point where comic book sales actually started to decline. In the 60s Marvel started publishing more lighthearted comics, like The Amazing Spiderman, which pretty much jumpstarted the Silver Age of Comics, and saw them come back into public eye, but I digress. Also, I believe baseball cards started to gain traction around that era, as well. And books, of course. And radio shows, and newspapers.