My college has some combination course/forum software (Canvas, if you want to know). The only forum thread ( for my CS class was started by yours truly, and there are no replies. It's possible that other people use the private message system, and we look at the site to get assignments, but that's about it. I had a friend tell me about a class she took where forum participation was mandatory (with quotas for various actions), resulting in the predictable phoniness. The forum for my accounting class has no activity whatsoever.

So essentially, no one uses it as a social tool. I doubt young children would be that interested either. It would be hard to take seriously as a "fall back", either. The real fall-back is email and SMS.