The egg could be a magic egg. A poor girl finds it. When she touches it, it glows. Out of the egg comes a key. The key unlocks a hidden door in an old castle, and inside she finds treasures that change her life.
A wizard has an egg that he has been incubating for years. One day, the egg cracks open and a miniature dragon comes out. The dragon has the power to breathe fire that can turn things into gold. But it is very naughty and causes chaos in the wizard's tower until the wizard teaches it some manners.
An egg is left alone in a meadow. A storm comes. A little mouse takes the egg to its burrow to keep it safe. As the days pass, the egg hatches into a small snake. At first, the mouse is scared, but then they become friends and the snake protects the mouse from other predators.