Not the kids, but at least a fine for the parents or whoever filled the balloons with it. The kids didn't decide to purchase it for that purpose. Even if they did, parents are supposed to teach kids how to make responsible decisions. Either way, it falls on the parents (or maybe a hired entertainer).
I'm fine with recreational divers using it as well, but blatantly wasting it on open circuit is unconscionable.
Medical/Science/Industrial uses are also dandy. They generally don't just dump it to the atmosphere as quick as they are breathing in those fields. Rather the gas is kept and reused as much as possible.
Using it as a welding shield gas is questionable too. Not quite as blatantly wasteful as OC scuba diving with it, but still questionable. People use it for welding stainless when Hydrogen could be used in stead. It's also used for welding aluminum when co2 laser welding could do the job without wasting the resource.