Well said. Teaching children to share is unfortunately an entrenched child rearing methodology. I'm going to ask my wife to read this.
I teach my 2 year old son to exclaim "Mine!". I exclaim "mine" in reaction to his pouting when I take something of mine from him. When ownership is ambiguous sometimes I play fight to control a toy/food with my son, say "mine" with a grin, sometimes I let my son win. He yells "mine!" in response and laughs.