'being'/'are'

A question from Gary in Germany:

Hello I've got a question about the verb 'be'.

If I want to describe an action, I can say for instance: "The children are being very naughty" But can't I say "The children are very naughty" as well, can I?

So my question is when must I use 'being' and when can I leave it out?

Gary

Listen to the answer on http://www.bbc.co.uk/worldservice/learningenglish/radio/specials/1837_aae/page3.shtml