If you can't share, get the hell out of the park!
One of the things I liked about hanging out at a playground in LA was the fact that if your kid's toys were out for all to see, they were up for grabs to share with others. That is, unless the owner (kid) was playing with them. (Naturally) Needless to say that when I arrived in the Boston area and hung out at parks, I was shocked to find parents "sharking" their children's toys. It wasn't the children that had a problem sharing, it was the damn parents. I was like WTF? My son would walk over to a toy that was literally abandoned, and as he neared his new found object, some crunchy mama would be running over trying not to trip over herself saying, "hey that's so and so's toy/bike/scooter". Please people, let your child do the talking, would ya?