Personification is a figure of speech where human qualities are given to animals, objects, or ideas. There are quite a few examples of this concept in Tuck Everlasting. For example,
Outside, the night seemed poised on tiptoe, waiting, waiting, holding its breath for the storm.
In this quote the night is personified. Of course nighttime does not have a body, so it definitely can't tiptoe or hold its breath. The sentence is a wonderful sentence though, because it helps build some tension in the story.
Another example of personification from the story is this example:
The first week of August was reasserting itself after a good night’s sleep.
The first week of August can't do anything (let alone assert itself). A week is a measurement of time, nothing else. But the personification in this quote helps to sell the idea that the events of the book are somewhat fated.
One last example.
The ceiling swam with bright reflections, and sunlight streamed across the dusty, chip-strewn floor.
Ceilings can't swim. It could be full of stuff or contain many things, but not swim. Nonetheless, the personification here helps the reader imagine a full and vibrant ceiling.