This is how I understand it; Legally you don't need permission to photograph/video anyone (young or old) in a public place, and for private use. You would need permission (a release) from anyone identifiable in the picture if you wished the picture to be used publicly (i.e. in a magazine, on your website), but if it were to be used for/in a news article you don't need permission. The only case where this is not true is if your videoing could be classed as harassment.
I would be as blatant as possible whilst doing it, its only if you were caught doing it sneakily that people might suspect you of something.