He holds the record as the youngest person in MLB history to appear at third base.After graduating from Jesuit High School in New Orleans at age 16,[1] the Phillies signed Caballero to a contract worth $10,000.

[4] The Philadelphia Phillies signed Caballero as an amateur free agent on September 9, 1944,[1] the same year that fellow Whiz Kid shortstop Granny Hamner joined the organization.

[8] For the 1945 season, the Phillies sent Caballero to the Class-A Utica Blue Sox of the Eastern League, where he played in 130 games at third base, batting .272 with 132 hits, 9 doubles, and 10 triples.

[13] Most of Caballero's 1947 season was played at Utica as well, where he posted a .287 batting average, 114 hits, and 13 doubles while splitting time with Hamner at second base.

[18] Additionally, Caballero notched the team's only hit in a one-hit pitching performance by Brooklyn Dodgers starting pitcher Rex Barney.

[19] In the middle of the season, the Phillies promoted Caballero's former Utica manager Sawyer from their Triple-A farm team, the Toronto Maple Leafs of the International League, to replace Ben Chapman at the helm.

[25] Media reports speculated that the Phillies would challenge the Dodgers for the National League pennant,[26] and one of Caballero's most valuable roles as a utility player was as a pinch runner off the bench.

[27][28] In the second game of a July 25 doubleheader against the Chicago Cubs at Shibe Park, starting pitcher Roberts batted in the bottom of the ninth in a scoreless shutout.

[28] A single to center field by Richie Ashburn allowed the speedy Caballero to score from second and completed the doubleheader sweep for Philadelphia—Bubba Church having pitched a three-hit shutout in the first game earlier in the day.

He led off the inning with a single, scoring the first run of a seesaw come-from-behind rally[29] that ended with a 9–8 Phillies victory,[30] closer Jim Konstanty's 13th of the season.

[30] In the final game of the season, in which the Phillies defeated the Dodgers, Caballero appeared as a pinch-runner, replacing catcher Andy Seminick in the ninth inning.

He posted only a .186 batting average at the plate and hit his only major league home run, along with 3 doubles and 2 triples in 84 games played.

He lost memorabilia signed by Babe Ruth, Eddie Mathews, and Pete Rose in the flood, calling the hurricane damage "a catastrophe".