My one year old grandson recently showed he knows how to share already by giving me and everyone else in my household his cold.
I sat him on my lap the first morning after I had been up most of the night sneezing and unable to breathe. Here is what I told him as he looked at his Nana so seriously.
"so, lets talk about sharing ok? You can share if you ever hit the lottery. You can share if you get a big inheritance, you can share toys, you can share chocolate candy if you have some but don't EVER, EVER, EVER share a nasty virus with me again. K?"
He looked at me ever so seriously like he understood what I was saying then wiggled down to go play with his toys. I don't think he gets it.