At the very-very end of Fablehaven, Kendra and Seth's parents return from their cruise looking like over-stuffed turkeys, and they all go home together.
Let's hit the pause button and go in a little deeper. Kendra and Seth's parents still know nothing about the fact that the Sorenson grandparents are running a preserve for supernatural critters, nor do they know that their kids nearly died helping save the place (and in Seth's case, almost making a mess of things too big to clean up). They also don't know that Kendra has been touched by fairy-magic, to the point where she's able to see magical creatures without first drinking milk from the house-sized cow Viola.
When Kendra reflects on her time at Fablehaven, she thinks:
Many of her experiences here had been dreadful. She and her family had nearly been killed. And she had lost a new friend when Lena was returned to the pond… At the same time… So many aspects of Fablehaven were wonderful. Life would seem so dry after the extraordinary events of the past couple of weeks. (19.96-97)
So Kendra has survived the good, the bad, and the ugly elements of Fablehaven, and now she's sort of looking forward to what's next. Obviously she'll be coming back to Fablehaven… but when? And what'll happen to her in the meantime?