One of the things that helps in my program is to help them learn the difference between 'sharing' and 'turn taking' and making sure that the two concepts are consistently applied

Aka if there is only ONE BALL and you ask a kid to share it they are going to look at you like you have two heads cause sharing it means they have to 'give it up' and well that is going to result in some crying and a tantrum cause chances are they are not ready to give it up ... however if you tell the child 'when you are done Sally would like a turn with the ball' they are much easier to comply ... cause that makes sense to them in their little world and kids are so LITERAL at this age. If they are having trouble being FAIR about turn taking than I will use visuals like a egg timer or something to help them regulate how long a turn each child gets with a popular toy.

If a kid has 50 blocks and is trying to hog them all than you can explain 'it is nice to 'share' because you have lots of blocks and Sally has none how would you feel if you wanted to build and Sally would not share the blocks with you' and tie in the empathy and so forth.