Fantasy vs Reality

The Tooth Fairy (or  in our case the mouse), Father Xmas, magic... these are all the familiar fantasy realms we are familiar with that fill our children's minds with a sense of wonderment and splendor. But there are more comples lines between feeding into the fantasy and teaching the reality. With Bilaal now entering the age of reasoning and the need to understand things... you know... the what, when and why age... I am constantly battling with this line.

For instance Bilaal will often ask me about the programmes or adverts he watches on T.V.
Is it real?
Are they really doing that?
Can I go there?
etc, etc

So when do i go with him on that ride of fantasy and say, yes the magical forest in the Baker's biscuit advert where all magical creatures steal the biscuits falling out of the childrens buckets is real...
or should I endeavour to teach him about the principles of marketing and not trusting and believing everything on t.v. when some beer advert makes it look like drinking it will make it snow.

Or maybe he shouldn't watch so much T.V?
But the thing is he doesn't, and its not just t.v. I want him to be a child and believe that magic is real and that wonderful things can happen if you just use your imagination, but I also want him to learn about the world and how it works.

Aah parenthood...