Justin and the Magic Stone by Dale Boyer

When Justin moves to a new home in a small town, he misses all his old friends, especially his best friend, Tom. But, one day, while he's out in the woods, he finds a magic, heart-shaped stone. With the stone in hand, he finds he can speak with all the animals around him! What's more, the stone also has the power to let him change size, and even travel through mirrors and telescopes to other places. Could the stone help him find his way back to his friend? What else might the magical stone do?