Good. If it takes a wakeup call like this to realise that somebody in that school screwed something up, then by all means, do it.
You and I, we don't know this kid. We have details in front of us and it's all we have to go on. We haven't been told the kid is an argumentative destructive piece of shit. We've been told he's had a hard life and can be difficult as a result.
Kids can be difficult in numerous different ways. It was a £1 soda. Phone home, tell his guardians, remind him it needs to be replaced. But essentially force the manual labour on him for something that wasn't actually destructive in the technical terms of the word? No.
A kid is a kid. This kid, he's had a shit life (by the sounds of it), he's got a lot to cope with, he's probably stressed to the eyeballs, and ultimately he wanted a soda, so he took it. You realise you don't get jailed in the UK, or at least where I live in the UK, for a first offence, especially if that offence is shoplifting? A caution, certainly. But not locked up, even just for a couple of days.
It strikes me that those saying this boy deserved what he got, also sound very akin to those saying disabled people deserve what they get, and you get forward by working whether you're able to or not. No, I'm not saying that you say those things, but ultimately, the world isn't so black and white as you may perceive it to be.
This isn't necessarily confidential information, either. We have no names, no name of the school, nothing. We're simply told a story that unless the OP had told us had come from his mother, could've easily come from the OP himself having seen it happen, or a friend in the same school.