Just told a quick story in the office about my young un the other day. I'm not discouraging this kind of thinking 
Discussion during dinosaur documentary (paraphrased):
He says lots of other funny stuff but this one stuck in the mind. Not bad reasoning for a 6 year old.

Discussion during dinosaur documentary (paraphrased):
Little un: Whats a carnivore daddy?
Daddy Gilly: Its an animal that only eats meat.
Little un: Like that big T Rex?
Daddy Gilly: Yep, just like that.
Little un: I eat meat too, am I one?
Daddy Gilly: No, you're an omnivore, we can eat anything
Little un: So why do you tell me off for eating my jumper?
He says lots of other funny stuff but this one stuck in the mind. Not bad reasoning for a 6 year old.