Haha, my 3yo knows how to make a basic filter (bucket, stones, gravel, sand, put pooey water in the top, come out cleaner) and all about all kinds of engines (and is desperate to see the big one at Kew - but that's because we let him watch Good TV, not cack Mark Williams' series re the Industrial Revolution is marvellous stuff - we all love it.
I love TV though. Mostly.