Arthur IS supposed to be a show that presents real life problems and gives useful morals and advice to today's children, with its interesting stories. But, yes, there IS a lot of unrealism...like the radioactive candy.

I think some examples of the unrealism are exaggerations...like the Big Boss Bar...no food is THAT unhealthy and strange, so the danger of the Big Boss Bar (with the radioactivity and the sparkles), in my view, was quite an exaggeration.
Many of them are those "How in the world does that happen?" occurences, like what happened to Ladonna, or like how Arthur lost El Boomerang in that one episode...the wind blew a pencil off the dresser, turning on a robot that bumped into the box and caused the soccer ball to fall out and somehow make its way down the stairs, off a jack-in-the-box, and out the window (I forgot how the whole process played out, but it was something like that)

However, I've noticed that many of the unrealistic things happening happen with technology...like Arthur's email reading ALOUD, "Toyguy22, you have no mail"...eventually to "No mail. *click* No mail. *click* No mail." Unless that email service has a speech system like Google Translate, it seemed unrealistic to me. Or Fern's phone with that annoying voice announcing aloud the battery reading in "Phony Fern". My guess is that they use those voices in the show's technology to tell the audience what's happening, as opposed to making them read some small text on a screen, which is what most people do.

So Arthur, I guess you can say, is a realistic show with some unrealistic happenings.