THATS MINE! brought to you by the never-ending peacemaker

That's mine!
I think every parent has heard this phrase over and over again. Do we have to buy multiple sets of everything? I feel like I have
had the same conversation at least 15 times a week with my girls. They know the deal, Share. Any toy is up for grabs, whoever is playing with it first wins. They can play for a while then they have to hand it over or play together. There is a few exceptions... they each have their blanket and their dolly that they sleep with, they can share if they want, but if the owner wants/needs it, it is automatically returned. It elates me when I see them figure it out on their own.
It took a while, but now the constant fights had subsided and together they shared wonderfully. They would help each other build huge block buildings and each knew who's turn it is to knock it down. If I give them a treat, they were ready and willing to share with their sister. On the playground they take turns with the other kids. Finally, they get it!
So last week, we decided to start doing child care again. Not to overwhelm ourselves we took on one boy. First day went fine, I think the idea of having this new boy in our house was a little strange to the girls and to him. The 2nd day was filled with fun, we went on a nature walk, played with the girls train set, colored, and hide and seek.
The 3rd day not so great. He brought his assortment of dinosaurs, my girls have never played with dinosaurs, they were excited for a new toys. It took about a whole 2 minutes after his Mom left, to hear those dreaded words! THAT'S MINE! followed by a screech from my daughter. He had promptly put all of his toys in a pile and flopped on top of them. This is mine! I understand completely about kids and their toys.
So I decided to not take away his toys. I am going to try to solve this one right now and show all of the kids how to share.
My first step was to explain to my children that he didn't have siblings so he really didn't learn about sharing yet. So we had to patient and teach him. I think my 3 year old got it, my 2 year old not so much.
Next step was my conversation with the dinosaurs, Yes I know... don't say it! The dinosaurs all agreed they wanted lots of friends to play with.
Step three... conversation with the dinosaur trainer... this was the long drawn out one.... the conclusion was 1. you can play with your toys, in a room by yourself, OR 2. you can play with the girls toys with everyone OR 3. you can share your toys, make the dinosaurs happy and play in the playroom with everyone!
His decision was #3 and off he went to the living room dinosaurs in hand.... it took all of 2 minutes for him to get bored and walk in, and say Here! YAY.... maybe this won't be as hard as I thought. Finally a victory!
I took my two year old to the potty and while washing hands, I hear my 3 year olds voice! THAT'S MINE!
At least I was within arms reach of the asprin!