When she was younger, celia didn't care if her brother took one of the cookies out of her bowl. now she is old enough to recognize that it is unfair for him to eat his share and take some of hers. at what age can children begin to understand the concept of fairness (and evidence of the development of conscience)?

I mean like you should start teaching them at an early age of what to do and what not to do if you want them to grow up right. For example; if their being mean to someone and their still young you should tell them, "No, be nice." and they will remember them words for the future. after a while they'll know what is nice and what is mean, ya know what I mean?