Are armadillos reptiles?
No. Armadillos are mammals, not reptiles. They are warm-blooded, and they feed their young on mothers' milk. Their hard covering is not made of the same sort of scales as reptiles' outer covering is.
Their direct ancestors are glyptodonts*, very much larger armadillos. Their more distant ancestors are thought to be general small mammals resembling shrews. Even further back their ancestry traces back through mammal-like reptiles and true reptiles, as do all mammals. *See image above of a glyptodont.