Family and home
When siblings argue over the same toy
When two children want the same building block at the same time, the sentence "you have to share" almost never helps. It ends the argument for thirty seconds and leaves two unhappy children behind. Both of them have lost something and neither has understood why.
Something else worked in our home. We practised sharing outside of the argument, in calm moments, with small and clear rules. First one child builds for two minutes, then the other. Children are good at this, as long as they are not angry at that very moment.
And then comes the most important part, which we adults often forget. When a child gives something up by itself, somebody should notice it and say so. Not with great praise, but with a simple sentence: that was kind of you. Children repeat what they are seen for.