The Birth (1981)

The first part of the documentary follows the development of a boy and girl, Jan and Suzanne, from birth to adulthood. At age 5, we see them getting into an open-air pool without swimsuits. They then play on the grass. Full rear and frontal nudity.

At age 10, we see them in 'Garden of Eden' type setting, where they share (presumably) their first kiss. Both are completely naked. Full frontal nudity including close-ups of their genitals.

At age 15, they are seen topless on a beach and then running, completely naked, through a field. Full frontal nudity.