Did you know that chickens and the big dinosaur called T-Rex are like family? That's because a long, long time ago, dinosaurs like T-Rex had babies that changed over many years. Those babies became birds, like chickens! So, even though T-Rex looks super big and scary, its family includes the chickens we see today.
Another way to say it is: "Chickens and T-Rex dinosaurs share the same family tree because chickens are the little relatives of the giant T-Rex from long ago."