T. Rex into bald eagle

My six-year old just asked if "Tyrannosaurus evolved into bald eagles"? Can someone recommend the best way of explaining this? (Presumably, he chose these two because they are the most striking in appearance to him).

"Evolved into" is a bad start, it suggests too much directionality or forward planning. For a six year old, if it were mine: No, the ancestors of birds, including bald eagles, were Jurassic dinosaurs, and the ancestors of T rex were some other Jurassic dinosaurs. This might lead to follow-up questions, and at some point you don't know the answer, so you can explain that we have ways to look up what is known, and that there are ways of trying to find answers to what nobody yet knows.

For a Kindergartner I'd say that's close enough.

Most dinosaurs are extinct, but all birds have a common ancestor that was a dinosaur. The archeosaurs are a group within the extinct dinosaurs that included a common ancestor of both T. rex and today's birds. The the bird ancestor probably belonged to the velociraptor group which is considerably more recent than the common ancestor with T. rex.

If our totally free-range domestic chickens (who easily outsmart our dog - who is bright as far as dogs go) are any example, I think the velociraptors must have been formidible predators, and had not the meteor that ended the Cretacious era and extinguished all the dinosaurs except the ancestral birds, I suspect they would have still been ruling the world.