Franz Robinson, the youngest son in the Swiss Family Robinson, is approximately six to eight years old during the initial shipwreck. In the family's early survival on the island, Franz aids his mother, Elizabeth, with domestic duties and housekeeping.

Over the subsequent decade, Franz matures and assumes increased responsibilities. He acquires practical skills through island life, eventually joining his father and older brothers on hunting expeditions. Described as the cherished "pet" of the family in his youth, Franz thrives in his island upbringing, his competencies shaping his character.

Ultimately, Franz chooses to leave the island. He accompanies his oldest brother, Fritz, and Jenny Montrose back to England. His youth motivates this decision, positioning him to adapt more readily to European life than his family members who remain. Some adaptations refer to this character as Francis rather than Franz.