The simple answer: no, your 5 year old should not be drinking coffee.
It negatively affects a child's nutrition, because caffeine acts an an appetite suppressant. Caffeine can also aggravates heart problems and nervous disorders.
Ask yourself this, why do you drink coffee? Is it not because you are restless if you skip your daily coffee dose? Keep in mind that caffeine is an addictive substance.
My kids are 8 and 10, and yes we occasionally give them half a cup over a weekend, if we know it's going to be a long day. We can definitely see how caffeine negatively affects their moods. It also affect negatively on their sleep patterns, even after a couple of hours of having coffee.
Although I love (and need) my daily cup of java, I will not let my kids drink too much of the stuff. In my opinion 5 is too young.
There was a study done in the US, read about it here:
http://www.chiro.org/ped...BSTRACTS/Caffeine.shtml
I also suggest the following:
http://www.vegetarian-nu...es/caffeine_effects.php