Tuck Everlasting by Natalie Babbitt

What if you could live forever? In this timeless story young Winnie Foster learns of a hidden spring in a nearby wood and meets the Tuck family, whose members reveal their astonishing discovery of the spring’s life-changing power. Now Winnie must decide what to do with her newfound knowledge―and the Tucks must decide what to do with her. But it’s not just the curious girl who is interested in their remarkable tale. A suspicious stranger is also searching for the Tucks, and he will stop at nothing until he finds them and uncovers their secret.