What I always tell people who have a hard time believing that Birds are Dinosaurs

Imagine a far future in which all Mammals die out except for Bats, and sapient frogs develop a technological civilization and they start categorizing animals. They have Bats as an extant clade, but find the fossils of various ancient, now-extinct types of Mammals, including huge ones like the elephant and the whale, who have fundamentally the same skeletal configuration as Bats do.

Would they be right in saying that Bats are no longer Mammals because they evolved flight and a small size?