Did Android 18 and Krillin have a kid?
Marron is the daughter of Krillin and Android 18; she is not identified by name until the very final manga installments, when a lot of time has passed and she has gotten much older. However, in the anime, she is referred by name numerous times throughout the Buu saga.
How old were Android 17 and 18?
Assuming their number designation could be a hint to their approximate age when they were introduced, as they were kidnapped as children, this would make both Android 17 and 18 in their late 20’s or early 30’s by the end of the Dragon Ball Super anime.
How did Android 18 and Krillin have a baby?
Android 18 isn’t exactly an android, she’s specifically a cyborg. She was human once but Dr.Gero remodeled her and added cybernetics. Gero left her human enough to conceive a child. And so she did with Krillin.
Why did Goten not have a tail?
Think about it this way; Gohan, Goten, and Trunks are each half-saiyan, half-human. They each have one fully Saiyan parent, with the genes for a tail, and one fully human parent, with no tail genes. So they’ve got a 50/50 chance of having or not having a tail.