I'm talking about the minimum wage, no barrier to entry, part-time-type jobs a kid might get over summer break for example.

While there's no denying the collateral lessons involving money management, driving, social skills etc., working at McDonalds or some department department store isn't going to teach a young person anything about responsibility; in fact, it probably reinforces the exact opposite message.

Doing the same menial task over and over again under surveillance while being micromanaged doesn't encourage responsibility or self-agency. It teaches kids that they can expect to graduate to the status of a consciousless tool after spending the first part of their lives learning and dreaming and trying to distinguish themselves for their personal qualities. Hard work doesn't actually pay off for most entry level jobs. Someone who shows up late and does the bare minimum will probably be better off in the long run.

The most harmful message for kids in particular is that these kinds of jobs diminish quality completely for the sake of quantity. More, more more. Faster, faster, faster. When is someone ever asked to take their time and do something better? When are they ever asked to think about what they're doing? Since there's already an established "way" of doing everything predetermined by the corporate bureaucracy, there is absolutely no room for reflection or trying different things. This undermines the basic premise which education tries to instill in young people.

Overall, I think working is probably a net negative for kids unless they're in a situation where they need the money, or they have connections for a job that relates to what they actually want to do with their lives. Otherwise I'd say it comes at a cost far greater than what they can expect to be paid.