This Land Is Your Land (known by every school child internationally)

I rather doubt that this is the case in many places outside the USA - where I believe the song is taught to every school child. Whether that constitutes 'living tradition' or not may depend on how you view, for instance, the formal teaching of old playground games, as opposed to just letting them carry on unmolested in the schoolkids' 'underground' (which is the whole point of those games if you ask me).

Old Dan Tucker, Dixie and Angelina Baker are good examples precisely because they're relatively old, and we can witness their adoption. Country Roads might be a good candidate (it has a very catchy chorus), but with the generation who first popularised it still very much alive, it's surely too early to say.