Other than your own living room at home, where do you go that has a TV just hanging around free for use? Coffee shops don't. Classrooms don't (certainly not enough for every student, at least). Parks don't. Trains/busses/airplanes don't. Backseat of the parents minivan probably doesn't, either.

Like where else can you use this other than a basically permanent installation at home for this to qualify as "taken everywhere by kids"?

there's less and less accessible ports. tvs are large, mounted high up and the cables aren't long enough to be comfortable.