Joy comes from within. It is a spark that all children have. The largest impact on a child's happiness is the previous generation's insistence on how and under which conditions happiness should be acquired.

A child who maintains their inner joy and protects it into adulthood is a person who is whole.

A person who has allowed their spark to die is missing an essential part of themselves.

Edit: test this for yourself- do you ever feel an emptiness, a hunger, an unease that cannot be satiated, an itch that cannot be scratched?