Brain Processes that Support Sharing
Why is sharing so hard for very young children? Like many aspects of development, it has to do with our frontal lobes (prefrontal cortex, in neuroscience-speak) according to research. The research which involved asking young children to divide up a pile of chips showed that the children understood the concept of sharing, but their ability to resist the temptation to keep the chips was not well developed. And this showed up in scans showing less activity in the part of the cortex that controls impulses and helps us make good decisions.
Our frontal lobes develop as we get older and as we practice using that part of our brains. Thus, cognitive training and modeling appropriate behavior can have a substantial impact.