By Example. Make sure they are aware of as many varieties of art, music, literature as possible. Point out the beauty in the smallest details, beauty in contrasts, and most important inner beauty.
By Example. You will teach your child many things. Comment on specific things you find beautiful, your child will learn from your example. Finding beauty everwhere is one of life's joys: a smile, a piece of art, poetic words, moving music, athetic physique, the natual world, complexity, and so on. Through your teaching your child will develop his/her own perception of beauty.
Children... ...Pick up on, and internalize, the admiration they feel from others for objects these others admire. If parents feel secure in their bodies, and admire each other, that will be picked up by the child as "my parents are beautiful", and form the foundation for future development of sense of beauty.