Tommy Shelby had children with Grace Burgess and Lizzie Stark ; the series later also reveals an illegitimate son with a woman named Zelda.

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Mother Child What the show says
Grace Burgess Charles Shelby Tommy’s first son with Grace, who later became his wife.
Lizzie Stark Ruby Shelby Tommy’s daughter with Lizzie, whom he later married.
Zelda Erasmus “Duke” Shelby A later reveal identifies Duke as Tommy’s firstborn son with Zelda.
In short: Grace gave him Charles, Lizzie gave him Ruby, and Zelda gave him Duke.