Johnathan Tate is the son of Larry Tate and Louise Tate.

Louise discovers she is pregnant (and informs Larry) in episode 12 of Season 1 entitled "...And Something Makes Three." There is no mention of Louise's pregnancy, Johnathan's birth, or Jonathan at all for some time after the announcement.

Johnathan's first appearance is in episode 4 of Season 2 entitled "My Grandson, The Warlock." Johnathan features heavily in this episode as Samantha's father Maurice mistakes Johnathan as the child of Samantha and Darrin and takes the child to show him off.