I'm a sucker for a good meme 
I've always been interested in politics (working class, union supporting parents)
The first time I remember my parents pointing out to be considerate of the source of a piece of information was when the miners strike was on and there was a LOT of footage of "violent aggressive unreasonable miners" on telly.
Myself or one of my siblings must have made a disparaging comment about the miners (being primary aged and knowing no better) and they both immediately pointed out there was very little footage of the police being shown, plus the footage was edited to show the most dramatic content (also time constraints) and that these were ordinary people just trying to feed & house their families. They pointed out the BBC was a govt controlled medium (despite they're supposed to be unbiased) and that itv was owned and controlled by people who were well off & privileged.
They'd have done it in language we understood at that age, but that was the gist.
My dad even now often quips "if its in the sun it must be true, but it's not the whole truth"
Here in Scotland I've been very impressed at what dd learned in a subject that isn't taught in England & wales (although I'm scots I did high school in England due to dad being in army) called Modern Studies.
It's an excellent subject that's very hard to describe in the context of an English.
It's a sort of mix of history, social history, sociology, politics, current affairs and media studies.
It basically teaches kids to not blindly accept what they're told by ANYONE, to think critically and openly and consider all possible perspectives.
Dd learned about things like how laws are passed (both in Scotland and Westminster), electoral systems & their pros and cons, rights & responsibilities, political bias in the media, how to assess the quality of a source of information...
I think it should be taught uk wide, hell worldwide really! (Tailored to each country of course)
I'd always discussed bias with her from a young age anyway.
I remember a very odd but proud incident when I overheard her telling a friend while still in primary school that she shouldn't believe a toy could do X because it seemed to in an ad. Because all adverts are for are to sell things and sometimes the ads are naughty and lie.