My wife is a teacher and, based on similar incidents she has related to me, I would agree that it is likely to be a result of a complaint from a child. That would explain why you have not been told any details. This is standard procedure to prevent the child in question being identified by the suspended person to prevent retaliation/witness silencing etc.
See this is the nuts thing, if the person in question was guilty, HE'D KNOW who it was accusing him, so keeping it quite does nothing at all. IN the case that someones innocent and being victimised by some student, he has no idea who it is, can't defend himself and as said, rumours spread as to why someones been suspended, no matter what happens most people tend to believe the no smoke without fire theory. Co-workers will likely never treat him quite the same and given a chance at promotion with two equally qualified people would they not remember the allegation and think he's a bigger risk.
The kid could be going around bad mouthing him to everyone, other kids telling their parents, the general stigma of peado or something being attached to someone never really goes so those that were innocent don't get over these things easily always.
This is what I hate about our modern world, entirely no common sense whatsoever. If its a kid accusing him, keeping him in the dark about the accusation helps no one, because as said if he was guilty he'd know who it was already and still be able to try and "shut him up" so who exactly benefits from him not being told, no one. Its the kind of thing that causes undue and completely unwarranted stress for no reason. Hell, I can even imagine co-workers who like whoevers been accused, and bosses being under stress because they are being told to not tell him, when they know full well if it were them being accused they'd want to know. It puts everyone under stress, makes work uncomftable and hostile for everyone. Just as the accused will probably always be thought of differently, the accused won't hold the same opinion of his co-workers and bosses who were happy to see him hung out to dry.
What happened to people communicating without accusations and lawyers and massive wads of red tape. Seriously where's the harm in calling him in, telling him whats going on, giving him the option to go home if he wants. If its a kid accusing him, the kid should probably be taken out of school and be at home with parents at this kind of time anyway so its not like they'll be upsetting the kid in school. If its using the network for porn, kiddie porn, something along those lines. Well removing them from the network isn't hard, but it also wouldn't take very long at all to have someone go through logs, files and search everything for evidence. Theres still no reason not to tell him.
Innocent till proven guilty, what a nice idea thats just completely dissappeared from our society in the past 20 years, does no one else see this is a massive step backward?