twinkle in one's daddy's eye

Etymology
From a song, "When You Were a Smile on Your Mother's Lips (and a Twinkle in Your Daddy's Eye)", written for the 1934 film, ; derived from the presumption that prior to the conception of a baby, the father was sexually aroused, and this arousal was reflected in a pleased look in the father's eyes.

Phrase

 * 1) Of a person, not yet conceived, particularly when referring to a time period preceding their conception.