NPR and PBS are both great and the equivalent of Canada's the CBC. There is of course the BBC (from Britain) and also ABC (Australian). Radio Netherlands and Radio New Zealand are both pretty great. These are all public broadcasting services with quality programming but with a different geographical focuses. Deutsche Welle which is the German world radio.
Al Jazeera has fantastic documentaries in its Witness series covering stuff from around the world (http://www.aljazeera.com/programmes/witness). Al Jazeera also has other really good programming and its focus obviously is the middle east. I think your pre-teens will benefit from being exposed from may public broadcasting services around. Our world is fascinating.
The Korean Broadcasting Service (KBS) has some fun travel/food shows while the rest is meh. The same with CCTV of China which has some cool travel pieces in China but overall it's programing is poor and it is the arm of the government and not a good source of information. Fun to check out once in a while though.
All in all, I think PBS, NPR, BBC CBC, Al Jazeera, Australian Broadcasting Company, and Radio New Zealand have the most to offer to a preteen as they have a full range of programming in English. The rest are worth checking out as an adult though because to me they are all interesting!
Follow Mothering