Recently where I'm from there was a strange man loping around the Elementary School playground. It was quickly dealth with, and there was even a lock down. Turns out the guy was sex-offender and a convict.
Now, you know more about this case than I do. But I'm a bit bothered by how you've chosen to phrase it. In some jurisdictions, "a sex offender and a convict" could describe a guy who was once arrested for public urination and who served jail time for a completely unrelated offense. It doesn't automatically make somebody a danger to children. Now, if the guy had been convicted of pedophilia specifically or something along those lines, that's a different matter, of course. I'm hoping that's the case here rather than you making snap judgments based on broad, scary labels.
Why was he there? Well, some niavie genius decided that it would be okay for Convicts to do community service in the nearby School Bus Depot, which is literally just across the fence from where all the children play... I'm proud of the kids for being cynical and staying away from the guy and the teachers for responding judiously. Some goofball who think to high of humanity should have his wig ripped off and thrown in the slammer himself, I say. Who in their right mind allows that? A child could have been kidnapped...and worse.
OK, fair enough (with the caveat I've given above). I'm not stupid enough to go on school property during school hours (if only because I'm all too aware of what that looks like) and somebody who does is indeed quite suspicious. Still, I don't have all the facts here. For instance, did he give any reason for being on school property? What testimony did the kids give? Again, you know more about the case than I do, I presume, but what you've given me isn't enough for me to say more than "Yeah, that's pretty suspicious."
There is a reason cops can be harsh. They see crap we don't see. It's easy for them to become skeptical of you.
That does not excuse the current situation where the vast majority of the American public is not fully aware of their rights and the trouble they can get into if they don't exercise them properly. "I've seen some shit" isn't an excuse to try to send potentially innocent people to prison. Isn't there a saying, something like "I'd rather let a guilty man walk free than send an innocent man to prison"? Unfortunately, that isn't how the police system is designed.
It also doesn't excuse mass hysteria. Did you know that the vast majority of pedophiles don't prey on random kids, but rather friends and family? That's right, Uncle Bob is more likely to be a threat to your kid than some random guy on the street. And, if I recall correctly, this sort of problem has been at an all-time low in recent years, but you'd never know it from the media. I'm not saying it's wise to trust random people on the street, of course, just that people tend to get worked up over nothing.
But still, the law system clearly says you are innocent untill proven guilty.
What that means in a legal context and what people normally consider it to mean are, sadly, different things. If you are arrested, in the cops' eyes, you are guilty, guilty, guilty. They don't have to, and won't, treat you as innocent. If you were innocent, you would not be there. They will concede to you the rights you are guaranteed by the Constitution and no more. Sometimes they will even try to violate those if they think they can get away with it (though I would hope this is in a small minority of cases).
All "innocent until proven guilty" means is the burden of proof is on the prosecution, and that you cannot infer guilt from refusal to answer questions. In particular, it doesn't protect you from unintentionally giving said prosecution all the ammo they need to convict you, whether or not you actually committed the crime. Judges and juries also tend to be biased against defendants; unless the prosecution has a particularly weak case, they will tend to assume that, again, you must be guilty or else you wouldn't be there.
