What comes before reading, 'riting, and 'rithmetic? Sharing.
Little Suzie has a brand new toy and Little Maggie comes along and decides she wants to play with it too. Suzie protests. You know what comes next, "Suzie, why don't you share with Maggie?" "How about you take turns?" "Suzie, be nice to the other children." -- as though Maggie had any right to Suzie's toy in the first place.
If Suzie values Maggie's friendship and gets enjoyment from allowing her to play with her new toys, Suzie will choose to share with Maggie. But if she chooses not to, has she committed a grave sin? If the toy is Suzie's property, she has exclusive rights to it. Why should she be required to give up those exclusive rights against her will?
Should one of a child's first lessons be that she must relinquish her property to other children merely because of their envy?
Instead of teaching sharing, maybe we should teach property rights and negotiation. Suzie, if you don't want to share, you don't have to. It's your toy. Maggie, if you'd like to play with Suzie's toy, you can try offering her one of yours to play with in exchange, but remember, Suzie has no obligation to accept your offer. If it's worth it to you, you can try to make her a better offer, and if not you can walk away. Sharing will not be a part of my children's curriculum.