Balance is a concept that only develops with age and experience.

If a child understood the concept of balance well, he or she would not develop. Imagine a child who avoided happy things because he or she knew they would be balanced later.

Balance is a bridge between dualism (e.g. "people") and spiritual ideals.

It isn't something any person can capture or describe, but has to be hunted as an unknown that continually evolves. If you find a reliable balance in something your natural reaction will usually be to profit from your realization, but nature will correct you.

Balance is cultivated either by experience or observation.

Just as a person can learn that scorpions sting either through experience, or by watching others' experiences with scorpions, balance is an objective wisdom that anyone will develop eventually.

Should it be deliberately cultivated?

The absolute ideal, in every kind of learning, is to learn quietly, alone, and without deliberate effort. Life as the teacher. The child who never talks, except to ask good questions out of curiousity, will be the smartest, but will get scars. Cultivating balance as part of a tradition (e.g. religion) is fine but ultimately balance is not a group pursuit.