...of animals give birth to live young.
No species of bird does (We aren't sure why - it would be an advantage to ostriches and rheas).
Only about 12 species of frog have even managed internal fertilization (meaning the sperm goes into the uterus instead of both eggs and sperm being released into water). Frogs, even the ones that do seem to manage it somehow, don't have penises or anything useful for pushing sperm into a uterus.
A few species of African frogs, all in genus Nectophrynoids, do give birth to live young, little tiny froglets. And Australian gastric brooding frogs swallow their own eggs and brood them in their stomachs for eight weeks (the females are pretty thin by the end).
But until now, no species of frog had been found that gave birth to tadpoles. Limonectes larvaepartus on the island of Sulawesi does just that...perhaps because some predator would make eggs too vulnerable.
Frogs also have some other interesting reproductive talents:
Strawberry Poison Dart Frogs lay their eggs on land and then carry the tadpoles to water-filled plants that grow in the trees. The mother will then lay even more eggs...unfertilized ones...into the otherwise empty pond to feed her tadpoles.
Darwin's Frog males keep their tadpoles in their vocal sacs.
Surinam Toad fathers carefully place the eggs on their mate's back...where the skin grows over them. They then emerge from mommy's back as froglets.
(Relevance to science fiction? Can you imagine a sentient alien race that used any or all of these tactics?)