Do you use the FB app or just your web browser? If the app, then maybe a reboot or dump the data and reconfigure. Your son should be able to do either of those and maybe already has. For the browser version, all I can think of is dumping cache and, again, I imagine your son has thought of that. I'm unfamiliar with the FB app (I abandoned FB years ago) so it's hard to troubleshoot beyond that.
