How honest should parents be?

[Kingpin]

In you're opinion whether you're a parent or not, how honest should parents be with their children when teaching them about life in this world?

Do you think children deserve a little chill out time not having to worry about global warming, sex, drugs, death, religion and money? 

Or just teach them everything you know right away.

Surely most people would say the best way is somewhere inbetween total insulation from the real world while at the same time not telling them all the mentally disturbing facts about the world too soon?

There should only be one lie. Santa exists and that should teach them the one lesson that you can't even believe what parents tell them all the time.
Teach the truth but at a level they will understand.
If they ask about where babies come from  telling them all the ins and outs is apparently frowned on.

Well in some circles yes it's frowned upon, but that's what I meant by age appropriate responses.  Something like where babies come for a 5 year old just isn't going to grasp all the biology.  When they are 11 or 12 they can understand and grasp it much better so the response can be very different.  I always find its best not to give long winded answers and don't give them more than they asked for.  Answer the question, short and honest and let them ask more if they want to.