LIFE magazine introduced its readers to an incredible nine-week-old baby named Julie Sheldon in 1954. She lived in Los Angeles and was, based from LIFE, the "world's youngest swimmer." She was diligently coached by her grandmother, a children's swimming instructor. LIFE wrote "Julie practices once a day," and, "faithfully following her morning nap with a 20-minute dip."

In June 1955, after year-and-a-half, LIFE published a follow-up article on Julie. They featured the then-19-month-old wonder to have progressed from mere swimming to deliberately playing with toys—from a tricycle to a teeter-totter—that her grandmother intently kept "on the bottom in the 4-foot depths" of the pool.

H/T Time