The Enormous Egg by Oliver Butterworth
 
This is the story of a boy named Nate Twitchell who takes care of an enormous egg laid by his hen Henrietta. What hatches from it? A dinosaur! The baby triceratops is named after Nate's great-great uncle,"Uncle Beazley."

From the minute word of Uncle Beazley gets out, people of all sorts start flocking to Nate's house. A whiskey distiller wants the triceratops for advertising, while a luggage maker wants to turn Uncle Beazley into a set of dinosaur suitcases. Nate gets a lot of help taking care of Uncle Beazley from a vacationing paleozoologist named Dr. Ziemer. Together they try to keep Uncle Beazley safe.

 
When the triceratops grows too large for Nate's home, Dr. Ziemer suggests a move to a safer place-the National Museum in Washington, DC. Once there, though, they face a new problem. Senator Granderson wants to turn people against Uncle Beazley so he may kill the dinosaur and become a hero. It falls to Nate to save his pet dinosaur.  
This is an excellent story that is about more than just the importance of science. It is also about patience, open-mindedness, and standing up for what you believe.  

Favorite parts of the story:

Nate's experience in Washington and his early morning walks Uncle Beazley.

How Dr. Ziemer treats Nate like an adult.