Aang has already died at the start of The Legend of Korra, but he had three children with Katara who appear in The Legend of Korra—Bumi, Kya, and Tenzin.
If you don’t believe me about Tenzin, then watch Avatar: The Last Airbender again and pay close attention to Aang and Katara.
Bumi is a nonbender, just like his uncle, Sokka (though, he did get airbending abilities in Book 3 of Korra).
Kya’s a waterbender, like her mother, and Tenzin’s an airbender, like his father.