Personally (JMO!), I think 3 is a little young for pocket money. I don't think most kids "get" the concept of money just yet. They may know that you can spend it on stuff, but they don't quite grasp the concept of it having "value"
I do think it's a perfect age to start with light chores (putting toys away, clearing something from the table), but I think positive feedback is a better reward.
Once they can appreciate saving it, I think its a good time to incorporate earning money. It's also nice to be able to have a good basis of doing chores because you are a family member, and add earning money for extra chores on top of that.
With my step-son, we didn't add money to the mix until about age 8. But I'm sure his dad could have done it sooner. (That was around when I entered the picture.) However, inflation has kept up with us. For about 6 months, he couldn't get enough of chores that paid $1. Now, it takes about $5 to pique his interest. He has to work for at least an hour, complete a task, and do it in a way that it is less work for us (key point!) to earn that amount. Things like washing the cars or washing all the windows.
Again, JMO!