When there’s fairness, sharing promotes health and well-being.
When there’s not fairness, sharing turns into an ownership/jealousy situation.
Some children are natural sharers. Some need to be taught. Some never learn. RealLife(tm) – often by 7 yrs old, is when natural alturism (where it exists), abruptly ENDS.
Socialization with peers.
Sometimes it ends sooner, depending on the family environment, at least in those cases where alturism would have existed naturally due to the nature of the individual’s temperment.