What age should a child be to practice a Martial Art? Some Clubs let Children join aged 3yrs old. Does this seem right?

I reckon that 3 is too young, but in general it depends on the child. If they really want to be there and pay attention and want to learn, then fine. If not, you end up running a very reasonably priced creche.

Some clubs don't care, its all about the money

We could fill our School with 3yr olds, but then it becomes a nursery? and for the money!

Do you think that a child can really know Karate?
I started to think about this after watching one of those clips on Youtube, the ones with the brilliant Karate kids.
They know the techniques, they have good stances, and have excellent flexibility, but do they know the purpose of Karate?
Ikken Hisatsu- To kill with one blow. I would suggest that the vast majority of children are unfamiliar with this concept, (Probably a good thing), but is Karate really Karate without this? As pleasing as good form is to watch, surely it is hollow, without true Karate spirit- In every technique, not just at the Kiai points.
What are your thoughts on this?