Rather than just saying "share" to them and then carrying on talking?
I've namechanged so I'm not identified BTW. A couple of days ago I went to a friend's house with my little boy, who is 20 months. My friend has a little boy aged 3 and a half.
To cut a long story short, the entire time we were there, my friend's DS wouldn't let my DS play with or touch a single toy. Every thing he picked up or started playing with, my friend's DS would snatch it off him or push him over, shouting "NO, IT'S MIIIIIIIINE". So my DS ended up with nothing to play with. He went and found a little book and my friend's DS wouldn't let him have it either and hit him.
Now it didn't particularly bother my DS, and it wouldn't bother me either if my friend had IMO disciplined her son properly. All she said when he had these outbursts was "Share nicely boys" and then carried on talking. When my older children were little and going through the not sharing phase, I would actually have taken the toy off them and given it back to whoever had it first, and made them have some time out if they'd hit or screamed in the face of the other child.
I mean, "share" is just a word isn't it? Unless you actually physically show a child what sharing is, they don't learn or understand it. BTW this boy is like it round my house with my son's own toys, and if we go to playgroups etc too. If my DS goes on anything such as a trampoline or ride on he will be there screaming in his face and pushing him off. Just to add I do take things off him for my DS to play, wherever we are, if he won't let DS have anything "Can X play with this? He needs something to play with". But obviously I can't be too harsh with someone else's child.
It's putting me off my friend as we clearly don't share the same ideas about discipline, and I think why the heck should my son have to put up with that?